- Email: [email protected]
Compressive strength of masonry grout containing high amounts of class F fly ash and ground granulated blast furnace slag
Construction and Building Materials 94 (2015) 719–727
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Compressive strength of masonry grout containing high amounts of class F fly ash and ground granulated blast furnace slag Fernando S. Fonseca a,⇑, Robert C. Godfrey b, Kurt Siggard c a
Dept. of Civil and Environmental Engineering, Brigham Young Univ., 368 Clyde Building, Provo, UT 84602, United States Caruso Turley Scott Inc., 1215 W. Rio Salado Parkway, Suite 200, Tempe, AZ 85281, United States c Concrete Masonry Association of California and Nevada, 6060 Sunrise Vista Drive, Suite 1990, Citrus Heights, CA 95610, United States b
h i g h l i g h t s Masonry grouts with fly ash and slag replacing high amounts of cement is discussed. A model is presented that describes the strength evolution of masonry grouts. Grouts with up to 55% ash and 85% ash–slag can be treated as conventional grout. Ternary mixes achieve higher ultimate strengths than binary and cement only mixes. Results show a viable alternative to make masonry more economical and sustainable.
a r t i c l e
i n f o
Article history: Received 2 March 2015 Received in revised form 18 June 2015 Accepted 14 July 2015 Available online 18 July 2015 Keywords: Fly ash Ground granulated blast furnace slag Compressive strength Cement replacement Grout Masonry Supplementary cementitious materials GGBS Strength development Partial replacement GGBFS High-volume fly ash
a b s t r a c t A large testing program was devised to determine the compressive strength of masonry grouts made with various combinations of class F fly ash and ground granulated blast furnace slag to replace high amounts of Portland cement. In a first phase, mixes were proportioned by volume and batched with 0, 20, 30, 40, 50, and 60 percent Portland cement replacement; specimens were cured in a dry and wet environment. The objective of the first phase was to determine the viability of and the methodology for the overall project. In the second phase, mixes were proportioned by weight, the more common practice in the United States, and batched with 0, 20, 30, 40, 45, 50, 55, 60 and 65 percent Portland cement replacement. Specimens in the second phase were cured in a wet environment only. In the first and second phases, Portland cement was replaced only by fly ash. In the third phase, mixes were proportioned also by weight and batched with 0, 50, 60, 65, 70, 75, 80, and 85 percent Portland cement replacement. In the third phase, Portland cement was replaced by combinations of fly ash and ground granulated blast furnace slag; however, the fly ash content was maintained constant at 25 percent. Specimens in the third phase were also cured in a wet environment only. Specimens were typically tested at 14, 28, 42, 56, and 90 days; in Phase I specimens were also tested at 7 days but not at 90 days. Three specimens were tested for each replacement rate, age, and curing conditions. Several mixes developed satisfactory strength, i.e., the mixes achieved the ASTM specified minimum compressive strength of 13.8 MPa at 28 days. The results show that mixes with up to 55 percent fly ash and 85 percent fly ash-ground granulated blast furnace slag substitutions reached the minimum compressive strength required at 28 days. Mixes with up to 60 and 65 percent fly ash achieved the minimum compressive strength of 13.8 MPa in 44 and 54 days, respectively. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction The use of concrete masonry is a popular form of building construction worldwide. Heightened concerns for the environment as ⇑ Corresponding author. E-mail addresses: [email protected] (F.S. Fonseca), [email protected] (R.C. Godfrey), [email protected] (K. Siggard). http://dx.doi.org/10.1016/j.conbuildmat.2015.07.115 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved.
well as the ever present economic pressures on new construction have prompted a study to replace Portland cement (PC) in masonry grout with both fly ash (FA) and ground granulated blast furnace slag (GGBFS). Concrete masonry has many proven sustainable benefits including low maintenance requirements, long life cycle, high recyclability, high reusability potential, and lower energy cost over life span. The concrete masonry industry could become even more
720
F.S. Fonseca et al. / Construction and Building Materials 94 (2015) 719–727
sustainable by reducing the use of PC, which, besides being the most expensive component in grouts, is manufactured using a high-energy process that generates approximately one ton of carbon dioxide per produced ton [1]. A possible way to achieve the lofty goal of making concrete masonry more sustainable is to increase the substitution levels of FA and GGBFS for Portland cement in masonry grout—low substitution levels have already been used for many years. For example, a 50 percent GGBFS replacement, a common amount in the US concrete industry, reduces carbon dioxide emissions by approximately one-half ton [2]. Furthermore, grinding slag for cement replacement uses approximately 25 percent of the energy needed to manufacture Portland cement [3]. High volume replacement of PC will most likely not cause a decrease in PC production (directly decreasing the production of carbon dioxide) but it may cause better use of available resources. Both FA and GGBFS are by-products of other industrial processes and ‘‘disposing’’ them in concrete and/or masonry products is an environmentally friendly alternative to more traditional disposal methods. In the case of FA replacement, there is also a significant cost reduction. While the concept of substituting PC with pozzolans and other mineral additives is not new, the use of such materials in masonry grout is new especially at the high levels replacement presented herein. There are several benefits of increasing the substitution levels of fly ash and slag for PC in masonry grout. These benefits may include using 100% recyclable materials, making construction more affordable because less expensive materials are used; reducing their disposal in landfills, ponds, and (in many places around the world) in river systems; and making possible construction industry expansion without increasing green-house gases emission. In addition, the use of these by-product materials may make masonry concrete construction more competitive and alleviate the demand for PC especially in developing countries where masonry construction is the preferred construction method. These benefits, however, can only be realized if these materials can be used without compromising building code requirements. The building code for masonry structures [4] specifies that the compressive strength of the grout must be equal or exceed the specified compressive strength of the masonry or meet ASTM C476 [5] specifications, which requires the grout to have a minimum compressive strength of 13.8 MPa at 28 days. A comprehensive research program has been completed to determine if the minimum masonry grout strength of 13.8 MPa, obtained from testing several hundred grout specimens, could be maintained with high levels of FA and GGBFS.
2. Hydration overview The hydration of PC is complex involving the hydration of several chemical compounds that results in the formation of various products. In general terms and using oxide or shorthand notation, PC hydration involves water and five main compounds: tricalcium silicate (C3S), dicalcium silicate (C2S), tricalcium aluminate (C3A), tetracalcium aluminoferrite (C4AF), and calcium sulfate dehydrate (CSH2) [6–8]. The main hydration product of PC is a calcium silicate hydrate (C–S–H), which does not have a definite stoichiometry but whose approximate formula is C3S2H8. In addition to C–S–H, the hydration process also forms calcium hydroxide (CH), which is a compound with a definite stoichiometry, Ca(OH)2, that may make up as much as 25 percent by volume of the hydrated cement paste [6,9]. Compared with the hydration of PC alone, the hydration of PC that incorporates FA and/or GGBFS is much more complex due to the coexistence of multiple interdependent and simultaneous
reactions [10]. The hydration reaction of the two calcium silicates C3S and C2S are very similar and generates essentially the same products; the difference being in the amount produced of each compound: two C3S molecules produce three CH molecules while two C2S molecules produce one CH molecule [6–8]. The two hydration products C–S–H and CH are the basis for the effectiveness of the FA and GGBFS. Fly ash is a fine-grained particulate produced through the combustion of coal. FA is precipitated from exhaust gases by means of electrostatic attraction, is considered a waste material, and is commonly used as a pozzolanic admixture in concrete [11]. FA adds compressive strength to the concrete by means of a secondary reaction with CH [6–8,12]. In general, siliceous glass in the FA reacts with the CH to form additional C–S–H. While this secondary reaction is slower than the primary reaction involved in the hydration of PC, the small initial sacrifice in compressive strength results in increased long-term compressive strength [6–8]. Among other benefits of using FA are improved workability and increased durability [6,8]. Blast furnace slag is a by-product of the iron and steel industry. Granulated blast furnace slag is formed when molten blast furnace slag is quenched in water. Grinding reduces the particle size of the granulated blast furnace slag to the same fineness as cement, and the resulting product, ground granulated blast furnace slag (GGBFS) is typically used as a mineral admixture in cement [10,13,14]. Unlike fly ash, GGBFS will hydrate directly to form C–S–H. This process, however, is very slow unless the GGBFS is activated by an alkaline compound such as CH [6,8,14], which is fortunately formed during the PC hydration. Activation occurs because CH breaks down a relatively impervious barrier formed around the outside of the slag during the initial stages of its hydration [14]. Theoretically only between 10 to 20 percent by weight of PC is required to activate the slag [6]. Compared to mixes with no cement replacement, mixes incorporating GGBFS have improved workability and slower compressive strength development but equivalent and even higher ultimate strength. 3. High volume FA and GGBFS concrete One of the first studies of high volume substitution of PC involved concretes containing up to 50 percent of FA [15]. The observations were that those concretes had lower temperature rise due to heat of hydration, were less prone to experience thermal cracking, and had generally low compressive strength at early ages. Since that pioneering study by Davies et al. [15], a significant amount of research has been conducted on concretes containing high volumes of FA [16–24] and high volumes of GGBFS [25–29]. More specifically, in the late 1980s, the concrete research group from the materials technology laboratory at the Canada Centre for Mineral and Energy Technology (CANMET-MTL) began developing a high-volume fly ash (HVFA) concrete [30]. HVFA concrete utilizes proper mixture proportioning and careful selection of materials to minimize the amount of PC while producing high-quality concrete. HVFA concrete has low PC content (225 lb/yd3 [155 kg/m3]), low water-to-cementitious materials ratio (w/cm) (190 lb/yd3 [115 kg/m3]) and incorporates up to 60 percent FA. Because of the low w/cm, however, superplasticizers may be needed to increase workability. Over the years, CANMET-MTL, in partnership with the Electric Power Research Institute, U.S.A., Canadian Electrical Association, and other public and private partners, has published a large amount of data on the properties of HVFA concrete [31,32]. HVFA concrete has been gradually gaining acceptance [33,34] among engineers and many significant structures have been build using HVFA concrete based on CANMET’s work [35], and today, research data exist from more than 25 years of their field performance.
721
F.S. Fonseca et al. / Construction and Building Materials 94 (2015) 719–727
The proven sustainable aspects and mechanical properties benefits of incorporating high volumes of FA and GGBFS into traditional concrete are leading researchers to explore new possibilities. One of the new frontiers being explored recently is the use of high volumes of FA and BBGFS in an attempt to make self-consolidating concrete more economical [36–39]. Another possibility, which is the new research presented herein, is the use of high volumes of FA and GGBFS in masonry grout. 4. Experimental program 4.1. Phase I The objective of this phase of the project was to determine the viability of and the methodology for the overall project. In this phase, the testing regime utilized only FA as supplemental cementitious material. The mixes were proportioned by volume and, in addition to the control mix (0% FA), mixes were batched with 20%, 30%, 40%, 50% and 60% FA. The materials were Portland cement Type II complying with ASTM C150/C150M [40], coal fly ash Class F complying with ASTM C618 [41], fine aggregate (sand) complying with ASTM C404 [42], 9.5 mm aggregate (pea gravel) complying with ASTM C404 [42], and potable water. The specific gravity (SSD) of the materials were 3.15 for the Portland cement, 2.33 for the fly ash, 2.59 for the sand, and 2.59 for the pea gravel. Six batches, one per grout mix, were made, and Table 1 gives the volume (V), the unit weight (UW), and the weight (W) for each material and the free water (FW) in the sand and pea gravel. Per ASTM C476 [5], individual cementitious materials and aggregates were first measured and then mixed with a mechanical mixer for a minimum of five minutes with sufficient potable water to achieve the desired consistency. The total water to total cementitious material ratio was 0.848, 0.779, 0.854, 0.795, 0.796, 0.819 for mixes 1 through 6, respectively. Grout slump was determined according to the procedure outlined in ASTM C143/C143M [43] and was 229 mm for mixes 1 through 4, 222 mm for mix 5, and 235 mm for mix 6. The temperature of the grout was measured as prescribed by ASTM C1064/C1064M [44] and was 24.8 (22.2), 24.0 (18.7), 30.0 (23.6), 25.1 (23.3), 26.3 (24.8), and 23.2 (19.1) °C for mixes 1 through 6, respectively; the numbers in parentheses are the ambient temperature. Due to the extent of testing undertaken, an alternative method for casting the grout specimens was adopted; such a procedure is allowed by ASTM C1019 [45]. The alternative method used herein provided the absorptive mold for the grout specimen as required by ASTM C1019 [45]. A non-absorptive plastic sheet was used a barrier between the specimens and floor of the laboratory, where specimens were cast. The specimens were made by filling the hollow cores of full concrete masonry units (CMU). The specimens were prepared in two lifts and consolidated by 25 blows of a tamping rod for each lift. The specimens were finished to produce a clean level surface and were then covered with a damp cloth for 24–48 h at which point the units were moved to their storage location. Half of the specimens were wet-cured and stored in a moist room complying with ASTM C511 [46]; half of the specimens were dry-cured and stored in a dry room complying with ASTM C157 [47]. The grout samples were removed from the CMUs by saw cutting them with a diamond blade two days prior of testing; specimens were returned to their storage location immediately after the saw cutting. Three specimens for each grout mix, test age, and curing condition were made. Specimens were tested in accordance with ASTM C1019 [45] at 7, 14, 28, 42, and 56 days and were capped prior of testing with high-strength sulfur according to specification of ASTM C617 [48]. The use of an alternative method to cast the specimens necessitated that the results of the compression testing be converted to results that would have been obtained if the specimens were cast using the standard casting method [45]. Due
to the objective of this phase, which was to determine the viability of and the methodology for the overall project, the results of Phase I, however, were not converted to ‘‘standard’’ results. Results of Phase I are summarized in Table 2 and plotted in Fig. 1. For the 0%, 20%, 30%, and 40% replacement rate, the wet and dry curing methods generally yielded similar compressive strength results except for the 0% and the 20% rate at 42 days. In these two instances, the strength of specimens dry-cured were lower than that of specimens cured in wet conditions. The 0% mix did not experience an increase in strength from 28 to 42 days, which is an anomaly since strength should increase with age. Although the 20% mix experienced a small increase in strength from 28 to 42 days, the rate of strength increase from 28 to 42 days was significantly smaller than that from 42 to 56 days. The significantly different rate of strength increase can also be considered an anomaly since the rate of increase should have been more similar especially after 28 days. For the 50% and 60% replacement rate, the dry curing method yielded slightly higher strengths than the wet curing method regardless of specimen age. Theoretically, there is enough water to ensure complete hydration without additional water being supplied if a mix has a water–cement ratio of 0.42 or greater [6]. Since all mixes in Phase I had water–cement ratio significantly higher than the theoretical ratio to ensure complete hydration, all mixes should have theoretically experienced complete hydration regardless of the curing condition; in other words, curing condition should not have affected the results. The slightly higher moisture content in the wet curing environment, however, could have adversely affected the compressive strength of the 50% and 60% replacement rate specimens. Despite these small discrepancies, the wet and dry curing methods yielded very similar compressive strength results. The specimens with 20% rate replacement achieved slightly higher strengths than those made with only PC. A small decrease in early concrete strength and then an increase, which may even surpass that of specimens with only PC have been observed by others [6,7]. The results of Phase I showed the viability of using high volumes of FA in masonry grout since specimens of all replacement rates and curing conditions, except for the 60% replacement rate, reached the minimum 13.8 MPa compressive strength at the specified 28 days. 4.2. Phase II The objectives of Phase I were to determine the viability of and the methodology for the overall project. The results of Phase I show that high volume substitution of Portland cement in masonry grout is viable and it does not compromise the grout compressive strength. The results also show that the wet curing method was slightly more conservative with two exceptions at one specific testing age. In Phase II mixes were proportioned by weight, a more common practice in the United States, instead of the easier volume proportioning used in Phase I. Besides the control mix (0% FA), mixes were batched with 40%, 50% and 60% FA using the same materials as those used in Phase I. In addition, other control mix (0% FA) and three mixes with 45%, 55%, and 65% FA replacement rate were batched; these four mixes used sand and pea gravel from a different source. The new sand also complied with ASTM C404 [42] and the new pea gravel also complied with ASTM C404 [42]. The additional control mix (0% FA) was batched to directly determine the effect of different aggregates while the other three additional replacement rate mixes were batched to better define the results between the different PC replacement rates. Table 3 summarizes the weight of the materials used and free water (FW) in the sand and pea gravel. The procedure used in Phase II to make the specimens was the same as that used in Phase I; however, three variations were made between batches 1 through 4 and batches 5 thought 8. Batches 5 through 8 were batches larger than batches 1 through 4 because the grout from batches 5 through 8 was used in another
Table 1 Material for batches – Phase I. Batch 1 (0% FA)
Cement Fly ash Sand Pea gravel Water
V (m3)
UW (kg/m3)
0.030
1505.7 1153.3 1167.8 1292.7
0.091 0.060
Batch 2 (20% FA) V (m3)
UW (kg/m3)
W (kg)
105.8 78.0 34.7
2.44 1.42
0.025 0.006 0.092 0.061
1505.7 1153.3 1180.6 1307.1
37.1 7.2 108.7 80.3 30.6
FW (kg)
V (m3)
UW (kg/m3)
W (kg)
3.24 1.76
0.016 0.016 0.099 0.066
1505.7 1153.3 1148.5 1297.5
24.7 18.9 113.8 85.6 29.8
45.6
Batch 4 (40% FA)
Cement Fly ash Sand Pea gravel Water
Batch 3 (30% FA)
FW (kg)
W (kg)
FW (kg)
V (m3)
UW (kg/m3)
W (kg)
2.25 1.46
0.023 0.010 0.099 0.066
1505.7 1153.3 1215.8 1299.1
35.0 11.4 120.5 85.7 32.7
FW (kg)
V (m3)
UW (kg/m3)
W (kg)
3.35 1.84
0.013 0.020 0.099 0.066
1505.7 1153.3 1171.0 1321.5
20.0 22.9 116.0 87.2 29.9
Batch 5 (50% FA)
V (m3)
UW (kg/m3)
W (kg)
0.020 0.013 0.010 0.066
1505.7 1153.3 1211.0 1319.9
29.9 15.4 120.0 87.1 30.9
FW (kg)
5.04 1.77
Batch 6 (60% FA) FW (kg)
3.42 1.73
722
F.S. Fonseca et al. / Construction and Building Materials 94 (2015) 719–727
Table 2 Compressive strength (MPa) results of Phase I testing. Mix type
Curing condition
Curing age (days) 7
14
28
42
56
0%
Wet Dry
13.6 13.6
15.7 15.9
18.7 18.1
21.2 18.1
21.5 21.5
20%
Wet Dry
13.0 13.2
15.2 15.0
21.4 20.8
24.4 21.7
25.5 24.9
30%
Wet Dry
9.6 10.4
12.7 13.0
15.3 16.0
19.8 19.0
18.8 18.1
40%
Wet Dry
9.4 9.8
12.0 12.0
16.3 15.5
18.2 18.3
18.8 19.1
50%
Wet Dry
8.2 9.3
11.0 12.4
13.9 14.7
16.3 18.7
18.1 19.8
60%
Wet Dry
4.8 6.1
6.8 8.0
8.1 9.7
9.2 10.6
8.9 10.7
research project involving wallettes. Also, in batches 1 through 4 a target slump was used while the total water to total cementitious material ratio was let to vary; in contrast, in batches 5 through 8 a constant total water to total cementitious material ratio was used while slump was let to vary. The last variation was that batches 1 through 4 were made in open air while batches 5 through 8 were made in a controlled environment. The total water to total cementitious material ratio was 0.795, 0.735, 0.843, 0.796 for batches 1 through 4, respectively and 0.972 for batches 5 through 8, respectively. Grout slump was 235, 235, 229, 229 mm for batches 1 through 4, respectively (the target slump was 229 mm.) For batches 5 through 7, the slump was 229, 241, and 267 mm, respectively; grout from batch 8 was flowable with a slump greater than 280 mm. The temperature of the grout was 27.1 (23.6), 15.8 (16.8), 24.7 (22.9), and 17.2 (17.8) °C for mixes 1 through 4, respectively and 22.2 (20.0), 22.2 (21.1), 22.2 (20.6), and 22.1 (20.0) °C for mixes 5 through 8, respectively; the numbers in parentheses are the ambient temperature. Since the hydration reactions of PC compounds are exothermic, the measured temperature of batches 2 and 4 appear to be wrong. These two batches were made in relatively cold days and possibly the readings were switched. The same alternative method for casting the grout specimens in Phase I was adopted in Phase II; but unlike the results of Phase I, the results of Phase II were converted as specified by ASTM C1019 [45]. Whenever an alternative casting method is used, ASTM C1019 [45] requires the results from the testing of those specimens to be converted to results that would have been obtained if the specimens were cast using the standard casting method. The conversion factor is determined by dividing the average compressive strength of 12 specimens cast using the standard casting procedure by the average compressive strength of 12 specimens cast using the alternative procedure. In order to determine the conversion factor for this research project, twelve specimens were cast using the standard specimen mold and twelve specimens were cast using the alternative mold. The specimens
cast using the alternative method were removed from the CMUs by saw cutting them with a diamond blade—the same procedure used during Phase I. All 24 specimens were tested using the same procedure as that of Phase I and the average compressive strength for the two groups were calculated; the conversion factor was determined to be 1.2. The results obtained for Phase II and presented hereon have been multiplied by the 1.2 conversion factor. The results of Phase II tests for the specimens from control mix 1 (replacement rate = 0%) and control mix 5 (replacement rate = 0%,new) are summarized in Table 4. The results are plotted in Fig. 2 with a linear regression model fitted to each set of data. The slopes of the linear regression models were used to determine if compressive strength results obtained using specimens made with control mix 1 were statistically different from those obtained using specimens made with control mix 5. Since the resulting p-value was 0.053, the null hypothesis of equal means was not rejected; in other words, there was no statistically significant difference between the compressive strength of specimens made with control mix 1 and the compressive strength of specimens made with control mix 5. Thus, the compressive strength values for mix 1 and mix 5, at each curing age, are grouped together and considered as the control mix. The average compressive strength for Phase II mixes are presented in Table 5 with the number in parentheses being the standard deviation. Values are also shown in Fig. 3 with standard deviation bars; the straight lines connecting the data points are simply shown for easier identification of the data. The strength at 14 days of specimens with 50% FA is higher than that of specimens with 45% FA and just slightly lower than that of specimens with 40% FA; at 28 days, the strength of 50% FA specimens is higher than that of 40% and 45% FA specimens. Either the strength of the 50% FA specimens is too high or the strength of the 40% and 45% FA specimens is too low. Dynamic effects, if any, would have been the same for all specimens since the loading rate was the same. In addition, slenderness and end restrains effects were also similar since the geometry of the specimens was similar with minor variations. Furthermore, theoretically a specimen cannot resist more load than its capacity, which eliminates the possibility of a too high experimental measured result. Thus, the strength of the 40% and 45% FA specimens are low. While the lower strength of the 45% FA specimens could be explained partially by the different aggregates used, the lower strength of the 40% FA specimens cannot. Possible reasons for the lower strength include faulty and/or non-parallel capping, misaligned end plates, FA flocculation, or a combination thereof. The strength of 45% FA specimens after 42 days is higher than that of 40% FA specimens. The same arguments presented above are also valid for this case, indicating that most likely the strength of 40% FA specimens is low. At early ages, the data shows that both the 45% and 55% FA specimens gained strength at a greater rate than the other specimens did. After 42 days a decrease in the strength gain rate is observed for both specimen sets; the decrease for the 55% FA specimens being slightly more pronounced. The data for the 50% FA specimens have what appears to be an abnormal value at 56 days. There should be a strength gain with increasing age but the strength of the 50% FA specimens at 56 days decrease in relationship with that at 42 days. Faulty caps, misalignment of the end plates, FA flocculation, or a combination thereof may explain the discrepancy. After 56 days, the strength of the 50% FA specimens is lower than that of the 55% FA specimens, suggesting that the measured results for the 50% FA specimens may be at fault.
Fig. 1. Compressive strength of mixes 1 through 6 – Phase I.
723
F.S. Fonseca et al. / Construction and Building Materials 94 (2015) 719–727 Table 3 Material for batches – Phase II. Batch 1 (0% FA) W (kg) Cement Fly ash Sand Pea gravel Water
Batch 2 (40% FA) FM (kg)
W (kg)
49.27 150.31 63.38 35.73 Batch 5 (0% FA) W (kg)
Cement Fly ash Sand Pea gravel Water
FM (kg)
W (kg)
10.39 5.27
W (kg) 90.61 110.74 654.36 276.85 183.94
10.39 5.27
W (kg)
FM (kg)
19.68 39.43 156.76 66.12 32.07
5.30 1.18
Batch 7 (55% FA) FM (kg)
147.65 120.81 872.48 369.12 245.24
Batch 4 (60% FA) FM (kg)
18.48 18.48 155.79 65.72 24.68
2.78 0.39
Table 4 Compressive strength (MPa) for replacement rates of 0% and 0%,new. Replacement rate
W (kg)
Batch 6 (45% FA)
268.45 872.48 369.12 245.24
FM (kg)
29.59 19.68 154.58 65.24 33.04
2.56 0.89
Batch 3 (50% FA)
5.64 1.52
Batch 8 (65% FA) FM (kg)
W (kg)
FM (kg)
65.77 122.15 619.81 258.39 171.67
7.79 3.95
7.27 3.69
Table 5 Compressive strength (MPa) results of Phase II testing.
Curing age (days) 14
28
42
56
90
0%,new
25.8 20.4 27.4
28.1 25.2 25.1
25.9 34.6 29.3
35.7 31.7 30.0
35.9 39.8 34.9
0%
25.1 22.6 23.4
27.9 27.1 28.2
28.4 28.5 28.0
30.2 29.2 30.0
33.0 31.8 32.9
Age
Portland cement replacement rates 0%
40%
45%
50%
55%
60%
65%
14
24.1 (2.5) 26.9 (1.4) 29.1 (2.9) 31.2 (2.4) 34.7 (2.9)
14.7 (1.2) 18.6 (0.9) 21.0 (0.2) 22.9 (0.6) 27.6 (0.6)
10.1 (0.4) 16.0 (2.1) 23.1 (2.9) 25.9 (0.7) 34.0 (5.2)
14.4 (0.6) 19.8 (0.6) 21.6 (0.3) 20.4 (3.4) 25.1 (2.2)
8.5 (2.0) 13.2 (3.6) 19.9 (0.1) 21.0 (1.3) 26.5 (2.3)
8.0 (0.3) 9.9 (0.1) 13.3 (0.3) 14.2 (0.7) 20.2 (0.2)
4.5 (0.4) 7.1 (1.0) 12.8 (0.7) 14.1 (1.3) 19.2 (0.6)
28 42 56 90
The strength evolution of concrete can be represented by Eq. (1) [49] reasonably well.
0
0
f c ðtÞ ¼ f c28
0
t a þ bt
ð1Þ
0
where f c ðtÞ is the mean compressive strength at age t days, f c28 is the mean 28-day compressive strength, and t is the age in days. The coefficient a has units of days and the coefficient b is dimensionless, and both coefficients are determined using a regression analysis. For each grout mix, the strength results were plotted and a model was developed. From the regression analyses, the coefficients a and b as well as the coefficient of determination, R2, were determined and are summarized in Table 6. The ratio of the coefficients a and b indicates the age of the grout (in days) at which one-half of the ultimate (in time) compressive strength of the grout is reached. The coefficient of determination indicates how well the actual data fit the statistical model; in other words, it provides a measure of how well the test results are replicated by the model. The coefficient of determination varies from 0 to 1 and
the closer the value is to 1, the better the statistical model replicates the measured strengths. As shown in Table 6, all R2 values are very close to 1, which indicate that the model can represent the measured compressive strength extremely well. The strength evolution curve for each mix is shown in Fig. 4. The explanation for the observed small discrepancies in the data has been given above. The slightly differences between the data presented in Fig. 3 and the data presented in Fig. 4 is due to the numerical procedure of fitting the statistical model. The procedure sometimes ‘‘pushes’’ the curve slightly up while it sometimes ‘‘pushes’’ the curve slightly down while trying to minimize the error between the model and actual data. Mixes with PC replacement rates of 60% and 65% did not reach the minimum compressive strength at the prescribed 28 days. The compressive strengths of these mixes at 28 days are 10.44 MPa and 8.29 MPa, respectively. The mix with 60% replacement rate reached the minimum compressive strength in 44 days while the mix with replacement rate of 65% reached the minimum compressive strength in 54 days. Since the materials used in making the grout tested are variable, directly
Fig. 2. Compressive strength of mixes 1 and 5 – Phase II.
724
F.S. Fonseca et al. / Construction and Building Materials 94 (2015) 719–727
Fig. 3. Compressive strength – Phase II.
Table 6 Regression and determination coefficients. Coefficient
a (days) b R2
Mixes 0%
40%
45%
50%
55%
60%
65%
6.024 0.7452 0.9914
11.00 0.5831 0.9892
19.65 0.2535 0.9976
8.923 0.7243 0.9849
17.62 0.3 0.9923
17.59 0.3196 0.9745
19.98 0.1446 0.9873
Fig. 4. Compressive strength – Phase II.
725
F.S. Fonseca et al. / Construction and Building Materials 94 (2015) 719–727 Table 7 Material for batches – Phase III. Batch 1 (25% slag) W (kg) Cement Fly ash Slag Sand Pea gravel Water
Batch 2 (35% slag) FM (kg)
21.59 10.80 10.80 135.35 56.11 24.18
W (kg)
FM (kg)
17.24 10.80 15.10 135.22 56.02 24.27
4.60 0.90
W (kg)
12.93 10.80 19.41 134.99 55.97 24.27
Batch 4 (55% slag) FM (kg)
4.59 0.90
Batch 6 (40% slag) FM (kg)
65.77 46.98 75.17 610.73 258.39 153.15
W (kg)
4.60 0.90
Batch 5 (30% slag)
Cement Fly ash Slag Sand Pea gravel Water
Batch 3 (45% slag)
8.62 10.80 23.72 134.76 55.88 24.22
FM (kg)
4.58 0.89
Batch 7 (50% slag)
W (kg)
FM (kg)
49.32 49.33 98.66 641.27 271.31 160.81
7.27 3.69
W (kg)
W (kg)
FM (kg)
29.60 49.33 118.39 641.27 271.31 160.81
7.64 3.87
7.64 3.87
Table 8 Compressive strength (MPa) results of Phase III testing. Age
Portland cement replacement rates 0%
14 28 42 56 90
24.1 26.9 29.1 31.2 34.7
50% (2.5) (1.4) (2.9) (2.4) (2.9)
19.9 22.8 25.2 34.5 38.7
60% (2.2) (2.5) (0.3) (1.1) (0.7)
22.5 22.2 31.3 33.3 37.3
65% (1.5) (0.6) (1.9) (1.1) (0.4)
20.5 24.0 35.6 36.0 41.9
extrapolation of the data presented herein is most likely to yield slightly different results when these materials are acquired from other sources. Thus, the results presented herein should be used in conjunction with a trial batch to verify the desired or expected grout properties made with different materials. 4.3. Phase III Combinations of FA and GGBFS were used to replace PC in Phase III. The GGBFS used conformed to ASTM C989/C989M [50] specification for grade 100. Seven mixes contained both FA and GGBS were proportioned by weight and were batched with 50%, 60%, 65%, 70%, 75%, 80%, and 85% replacement rate; the amount of FA was held constant at 25% while the amount of GGBS was progressively increased. The mixes with 50, 60, 70, and 80 were made using aggregates from one source while mixes with 65, 75, and 85 were made with aggregates from a different source; the two sources are the same as those used in Phase II. Furthermore, mixes for Phase III were made at the same time as those for Phase II; thus, the 0% and 0%,new mixes discussed in Phase II were common to Phases II and III. Table 7 summarizes the weight of the materials used and free water in the sand and pea gravel. The procedure used in Phase III to make the specimens was the same as that used in Phase I with the same variations made in Phase II; i.e., batches 5 through 7 were larger batches, used a constant total water to total cementitious material ratio, and were made in a controlled environment. The total water to total cementitious material ratio was 0.688 for batches 1 through 4 even though their slump were 229, 222, 216, and 222 mm, respectively. Batch 5 through 7 had a total water to total cementitious material ratio of 0.873 while their slump were 203, 216, 267 mm, respectively. The temperature of the grout was 26.1 (28.4), 27.9 (26.2), 28.7 (27.1), and 29.1 (27.8) °C for mixes 1 through 4, respectively and 22.2 (20.0), 22.2 (20.6), 22.2 (21.1), and 22.1 (21.1) °C for mixes 5 through 7, respectively; the numbers in parentheses are the ambient temperature. Since the hydration reactions of PC compounds are exothermic, the measured temperature of batch 1 appear to be incorrect; it is possible that the reading was switched. The same alternative method for casting the grout specimens in Phases I and II was adopted in Phase III and the results were converted to results obtained from samples cast using the standard grout specimen mold using the same 1.2 conversion factor determined in Phase II. Thus, the results presented hereon for Phase III were multiplied by the 1.2 conversion factor. The average compressive strength values for the control mix and for mixes in Phase III are presented in Table 8 with the number in parentheses being the standard deviation. Values are also shown in Fig. 5 with standard deviation bars; the straight lines connecting the data points are simply shown for easier identification of the data.
70% (4.3) (1.4) (1.4) (2.3) (0.2)
19.1 23.5 29.0 29.4 32.8
75% (0.5) (1.4) (1.9) (0.7) (0.3)
20.9 19.6 27.1 29.9 33.6
80% (1.0) (2.3) (0.8) (1.6) (1.6)
13.4 16.7 18.6 21.7 23.2
85% (0.8) (2.0) (2.1) (0.2) (0.2)
11.2 13.2 16.9 19.1 20.8
(1.0) (1.4) (1.0) (0.4) (0.2)
The results for the 60 and 75FS replacement rates have at 28 days what appears to be a discrepancy since the strength decreases from that at 14 days. Faulty caps, misalignment of the end plates, FA and GGBFS flocculation, or a combination thereof may explain the discrepancy. Also noticeable is the significant increase in strength from 28 to 42 days for mixes 60, 65, and 75FS and from 42 to 56 days for mix 50FS. The strength of mixes 50 and 60FS are low compared with that of mix 65FS, which may be partially explained by the different aggregates used. The results show a large decrease in strength for mixes with 80 and 85FS replacement rate. Models were also developed to represent the strength evolution of the mixes in Phase II. The model used is given in Eq. (1) and the regression coefficients a and b as well as the coefficient of determination, R2, for each mix are summarized in Table 9. The strength evolution curve representing each mix is shown in Fig. 6. Overall, mixes with up to 75FS replacement rate have a small decrease in early strength. Strength, however, increases with time and in many cases surpasses that of the control mix. It appears that the ultimate strength of mixes with up to 75FS replacement rate will be at least as that of the control mix. Even though there is a large decrease in strength for mixes with 80 and 85FS replacement rate compared to the strength of the control mix, these mixes did reach the minimum compressive strength of 13.8 MPa at the prescribed 28 days. The ultimate strength of these mixes, however, will be most likely lower than that of the control mix.
5. Conclusions The results of the experimental research herein reported lead to the following conclusions: 1. High volume FA and FA-GGBFS replacement of PC is a viable alternative to make concrete masonry construction more economical and sustainable. 2. Grouts made with up to 55% FA and up to 85% FA-GGBFS achieve the minimum grout compressive strength of 13.8 MPa at 28 days. In other words, grouts with up to 55% class F FA and a combination of 25% class F FA and 60% GGBFS can essentially be treated as conventional masonry grout. 3. Grouts with 60% and 65% class F FA achieve the minimum grout compressive strength of 13.8 MPa at 44 and 54 days. In cases where masonry structures may not need to achieve the
726
F.S. Fonseca et al. / Construction and Building Materials 94 (2015) 719–727
Fig. 5. Compressive strength – Phase III.
Table 9 Regression and determination coefficients. Coefficient
a (days) b R2
Mixes 0%
50%
60%
65%
70%
75%
80%
85%
6.024 0.7452 0.9914
13.11 0.4636 0.9583
8.886 0.5129 0.9643
11.9 0.4426 0.9792
9.139 0.6222 0.9952
8.553 0.5136 0.9547
9.732 0.6222 0.994
10.84 0.5178 0.9888
Fig. 6. Compressive strength – Phase III.
F.S. Fonseca et al. / Construction and Building Materials 94 (2015) 719–727
minimum strength at 28 days, the results of this research provide another viable option to engineers to make concrete masonry construction more economical and sustainable. 4. Results are slightly sensitive to the aggregate used; therefore, masonry grout mix designs incorporating high volumes of supplementary cementitious materials should be evaluated and tested and the results presented herein should be used in conjunction with a trial batch to verify the desired or expected grout properties made available materials. 5. Ternary blend (PC-FA-GGBFS) grout mixes can achieve higher ultimate compressive strengths that those of binary blends (PC-FA) and PC only grout mixes. Acknowledgements This testing program would not have been possible without the support of the following people and organizations: Paul Jahn from Ash Grove Packaging; David Anderson, Rodney Mayo, and David Wilson from BYU; Rick Child from Child Enterprises; Kevin Hatfield from Doyle Hatfield Masonry; Jim Johnson and Chris Bedford from Headwaters; Heath Holdaway from IMS Masonry; Rob Shogren and Todd Sherman from Lafarge; Dennis W. Graber, Nick Lang, Bob Thomas and Jason Thompson from National Concrete Masonry Association; Wade Ficklin, Paul Kamnikar and Gerald Travis from Oldcastle; Scott Hanks and Tyler Clark from Quikrete, and Brent Overson from Utah Masonry Council. The following BYU students helped during construction of the hundreds of specimens: Jacob Ballard, Zifan Guo, Juan Manuel Salguero Mendizabel, Brice Somers, and Scott Watterson. These students were supported financially by a generous Grant from the NCMA Education and Research Foundation. References [1] Hanle, L.J.; Jayaraman, K.R.; and Smith, J.S., CO2 Emissions Profile of the U.S. Cement Industry, http://www.epa.gov/ttn/chief/conference/ei13/index.html, 13th International Emission Inventory Conference, Florida, USA, June 8–10, 2004. [2] F. Hogan, J. Meusel, L. Spellman, Breathing Easier With Blast Furnace Slag, Rock Products, Cement Americas (2001) 11–15. [3] Chesner, W.; Collins, R.; and MacKay, M., User Guidelines for Byproduct and Secondary Use Materials in Pavement Construction, U.S. Dept. of Transportation, Federal Highway Administration, Research and Development, Turner-Fairbank Highway Research Center, Available to the public through the National Technical Information Service in McLean, VA, Publication Number: FHWA-RD-97-148, April, 1998. [4] Masonry Standards Joint Committee, Building Code Requirements for Masonry Structures (TMS 402-11/ACI 530-11/ASCE 5-11). The Masonry Society, Boulder, CO; America Concrete Institute, Farmington Hills, MI; Structural Engineering Institute of the America Society of Civil Engineers, Reston, VA. [5] ASTM C476-10, Standard Specification for Grout for Masonry, ASTM International, West Conshohocken, PA, 2010. [6] S. Mindess, J.F. Young, D. Darwin, Concrete, Second ed., Pearson Education Inc., Upper Saddle River, NJ, USA, 2003. [7] A.M. Neville, Properties of Concrete, Fourth and Final ed., Pearson Education Limited, Edinburgh Gate, Harlow, Essex CM20 2JE, England, 1995. [8] P.K. Mehta, P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials, Third ed., The McGraw-Hill Companies Inc., Two Penn Plaza, New York, NY, 2006. [9] Q. Zeng, K. Li, T. Fen-chong, P. Dangla, Determination of cement hydration and pozzolanic reaction extents for fly-ash cement pastes, Constr. Build. Mater. 27 (1) (2012) 560–569. [10] X.Y. Wang, H.S. Lee, Modeling the hydration of concrete incorporating fly ash or slag, Cem. Concr. Res. 40 (7) (2010) 984–996. [11] R. Helmut, Fly Ash in Cement and Concrete, Portland Cement Association, Skokie, IL, 1987. [12] Y.M. Zhang, W. Sun, H.D. Yan, Hydration of high-volume fly ash cement pastes, Cement Concr. Compos. 22 (6) (2000) 445–452. [13] S.C. Pal, A. Mukherjee, S.R. Pathak, Investigation of hydraulic activity of ground granulated blast furnace slag in concrete, Cem. Concr. Res. 33 (9) (2003) 1481–1486. [14] S. Song, D. Sohn, H.M. Jennings, T.O. Mason, Hydration of alkali-activated ground granulated blast furnace slag, J. Mater. Sci. 35 (1) (2000) 249–257. [15] R.E. Davis, R.W. Carlson, J.W. Kelly, H.E. Davis, Properties of cements and concretes containing fly ash, ACI J. Proc. 33 (5) (1937) 577–612. [16] M.R.H. Dunstan, Development of high fly ash content concrete, ICE Proc. 74 (3) (1983) 577–611.
727
[17] M.N. Haque, M.K. Goplan, R.C. Joshi, M.A. Ward, Strength development of inadequately cured high fly ash content and structural concretes, Cem. Concr. Res. 16 (3) (1986) 363–372. [18] D. Ravina, P.K. Mehta, Compressive strength of low cement/high fly ash concrete, Cem. Concr. Res. 18 (4) (1988) 571–583. [19] A. Bilodeau, V.M. Malhotra, High-volume fly ash system: concrete solution for sustainable development, ACI Mater. J. 97 (1) (2000) 41–48. [20] A. Bisaillon, M. Rivest, V.M. Malhotra, Performance of high-volume fly ash concrete in large experimental monoliths, ACI Mater. J. 91 (2) (1994) 178–187. [21] W.S. Langley, G.G. Carette, V.M. Malhotra, Structural concrete incorporating high volumes of ASTM class fly ash, ACI Mater. J. 86 (5) (1989) 507–514. [22] T.R. Naik, B.W. Ramme, Low cement content high strength concrete, Cem. Concr. Res. 17 (2) (1987) 283–294. [23] T.R. Naik, B.W. Ramme, High-strength concrete containing large quantities of fly ash, ACI Mater. J. 86 (2) (1989) 111–116. [24] D. Ravina, P.K. Mehta, Properties of fresh concrete containing large amounts of fly ash, Cem. Concr. Res. 16 (2) (1986) 227–238. [25] V. Sivasundarum, V.M. Malhotra, Properties of concrete incorporating low quantity of cement and high volumes of ground granulated slag, ACI Mater. J. 89 (6) (1992) 554–563. [26] T. Tomisawa, M. Fujii, Effects of high fineness and large amounts of ground granulated blast-furnace slag on properties and microstructure of slag cement, in: V.M. Malhotra (Ed.), Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, SP 153, American Concrete Institute, Farmington Hills, Michigan, 1995, pp. 951–971. [27] M. Elchalakani, T. Aly, E. Abu-Aisheh, Sustainable concrete with high volume GGBFS to build Masdar City in the UAE, Case Stud. Constr. Mater. 1 (2014) 10–24. [28] Richardson, D.N., Strength and durability characteristics of a 70% ground granulated blast furnace slag (GGBFS) concrete mix, Final Report RI99-035/ RI99-035B, Missouri Department of Transportation, February 2006. [29] Anderson, K.W.; Uhlmeyer, J.S.; Williams, K., Russell, M., Evaluation of portland cement concrete pavement with high slag content cement, Final Report WARD 728.2, Washington State Department of Transportation, October 2013. [30] American Concrete Institute Committee 232, Report on High-Volume Fly Ash Concrete For Structural Applications, ACI 232.3R-14, American Concrete Institute, Farmington Hills, MI, October 2014. [31] V.M. Malhotra, High-performance high-volume fly ash concrete, Concr. Int. 24 (7) (2002) 30–34. [32] N. Bouzoubaa, V.M. Malhotra, Performance of lab-produced high-volume fly ash cements in concrete, Concr. Int. 23 (4) (2001) 29–33. [33] D. Manmohan, P.K. Mehta, Heavily reinforced shearwalls and mass foundations built with ‘green’ concrete, Concr. Int. 24 (8) (2002) 64–70. [34] D. Cross, J. Stephens, J. Vollmer, Field trials of 100% fly ash concrete, Concr. Int. 27 (9) (2005) 47–51. [35] V.M. Malhotra, P.K. Mehta, High-performance, High-Volume Fly Ash Concrete for Building Sustainable and Durable Structures, Third ed., Supplementary Cementing Materials for Sustainable Development, Inc., Ottawa, Canada, 2008. [36] N. Bouzoubaâ, M. Lachemi, Self-compacting concrete incorporating high volumes of class F fly ash: preliminary results, Cem. Concr. Res. 31 (3) (2001) 413–420. [37] T.R. Naik, R. Kumar, B.W. Ramme, F. Canpolat, Development of high-strength, economical self-consolidating concrete, Constr. Build. Mater. 30 (2012) 463– 469. [38] G. Hannesson, K. Kuder, R. Shogren, D. Lehman, The influence of high volume of fly ash and slag on the compressive strength of self-consolidating concrete, Constr. Build. Mater. 30 (2012) 161–168. [39] K. Kuder, D. Lehman, J. Berman, G. Hannesson, R. Shogren, Mechanical properties of self consolidating concrete blended with high volumes of fly ash and slag, Constr. Build. Mater. 34 (2012) 285–295. [40] ASTM C150/C150M-12, Standard Specification for Portland Cement, ASTM International, West Conshohocken, PA, 2012. [41] ASTM C618-08, Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete, ASTM International, West Conshohocken, PA, 2008. [42] ASTM C404-11, Standard Specification for Aggregates for Masonry Grout, ASTM International, West Conshohocken, PA, 2011. [43] ASTM C143/C143M-12, Standard Test Method for Slump of Hydraulic-Cement Concrete, ASTM International, West Conshohocken, PA, 2012. [44] ASTM C1064/C1064M-12, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete, ASTM International, West Conshohocken, PA, 2012. [45] ASTM C1019-13, Standard Test Method for Sampling and Testing Grout, ASTM International, West Conshohocken, PA, 2013. [46] ASTM C511-13, Standard Specification for Mixing Rooms, Moist Cabinets, Moist Rooms, and Water Storage Tanks Used in the Testing of Hydraulic Cements and Concretes, ASTM International, West Conshohocken, PA, 2013. [47] ASTM C157/C157M-08, Standard Test Method for Length Change of Hardened Hydraulic-Cement Mortar and Concrete, ASTM International, West Conshohocken, PA, 2008. [48] ASTM C617/C617M-11, Standard Practice for Capping Cylindrical Concrete Specimens, ASTM International, West Conshohocken, PA, 2011. [49] ACI 209.2R-08, Guide for Modeling and Calculating Shrinkage and Creep in Hardened Concrete, Reported by ACI Committee 209, American Concrete Institute, Farmington Hills, MI, 2008. [50] ASTM C989/C989M-14, Standard Specification for Slag Cement for Use in Concrete and Mortars, ASTM International, West Conshohocken, PA, 2014.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Compressive strength of masonry grout containing high amounts of class F fly ash and ground granulated blast furnace slag Fernando S. Fonseca a,⇑, Robert C. Godfrey b, Kurt Siggard c a
Dept. of Civil and Environmental Engineering, Brigham Young Univ., 368 Clyde Building, Provo, UT 84602, United States Caruso Turley Scott Inc., 1215 W. Rio Salado Parkway, Suite 200, Tempe, AZ 85281, United States c Concrete Masonry Association of California and Nevada, 6060 Sunrise Vista Drive, Suite 1990, Citrus Heights, CA 95610, United States b
h i g h l i g h t s Masonry grouts with fly ash and slag replacing high amounts of cement is discussed. A model is presented that describes the strength evolution of masonry grouts. Grouts with up to 55% ash and 85% ash–slag can be treated as conventional grout. Ternary mixes achieve higher ultimate strengths than binary and cement only mixes. Results show a viable alternative to make masonry more economical and sustainable.
a r t i c l e
i n f o
Article history: Received 2 March 2015 Received in revised form 18 June 2015 Accepted 14 July 2015 Available online 18 July 2015 Keywords: Fly ash Ground granulated blast furnace slag Compressive strength Cement replacement Grout Masonry Supplementary cementitious materials GGBS Strength development Partial replacement GGBFS High-volume fly ash
a b s t r a c t A large testing program was devised to determine the compressive strength of masonry grouts made with various combinations of class F fly ash and ground granulated blast furnace slag to replace high amounts of Portland cement. In a first phase, mixes were proportioned by volume and batched with 0, 20, 30, 40, 50, and 60 percent Portland cement replacement; specimens were cured in a dry and wet environment. The objective of the first phase was to determine the viability of and the methodology for the overall project. In the second phase, mixes were proportioned by weight, the more common practice in the United States, and batched with 0, 20, 30, 40, 45, 50, 55, 60 and 65 percent Portland cement replacement. Specimens in the second phase were cured in a wet environment only. In the first and second phases, Portland cement was replaced only by fly ash. In the third phase, mixes were proportioned also by weight and batched with 0, 50, 60, 65, 70, 75, 80, and 85 percent Portland cement replacement. In the third phase, Portland cement was replaced by combinations of fly ash and ground granulated blast furnace slag; however, the fly ash content was maintained constant at 25 percent. Specimens in the third phase were also cured in a wet environment only. Specimens were typically tested at 14, 28, 42, 56, and 90 days; in Phase I specimens were also tested at 7 days but not at 90 days. Three specimens were tested for each replacement rate, age, and curing conditions. Several mixes developed satisfactory strength, i.e., the mixes achieved the ASTM specified minimum compressive strength of 13.8 MPa at 28 days. The results show that mixes with up to 55 percent fly ash and 85 percent fly ash-ground granulated blast furnace slag substitutions reached the minimum compressive strength required at 28 days. Mixes with up to 60 and 65 percent fly ash achieved the minimum compressive strength of 13.8 MPa in 44 and 54 days, respectively. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction The use of concrete masonry is a popular form of building construction worldwide. Heightened concerns for the environment as ⇑ Corresponding author. E-mail addresses: [email protected] (F.S. Fonseca), [email protected] (R.C. Godfrey), [email protected] (K. Siggard). http://dx.doi.org/10.1016/j.conbuildmat.2015.07.115 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved.
well as the ever present economic pressures on new construction have prompted a study to replace Portland cement (PC) in masonry grout with both fly ash (FA) and ground granulated blast furnace slag (GGBFS). Concrete masonry has many proven sustainable benefits including low maintenance requirements, long life cycle, high recyclability, high reusability potential, and lower energy cost over life span. The concrete masonry industry could become even more
720
F.S. Fonseca et al. / Construction and Building Materials 94 (2015) 719–727
sustainable by reducing the use of PC, which, besides being the most expensive component in grouts, is manufactured using a high-energy process that generates approximately one ton of carbon dioxide per produced ton [1]. A possible way to achieve the lofty goal of making concrete masonry more sustainable is to increase the substitution levels of FA and GGBFS for Portland cement in masonry grout—low substitution levels have already been used for many years. For example, a 50 percent GGBFS replacement, a common amount in the US concrete industry, reduces carbon dioxide emissions by approximately one-half ton [2]. Furthermore, grinding slag for cement replacement uses approximately 25 percent of the energy needed to manufacture Portland cement [3]. High volume replacement of PC will most likely not cause a decrease in PC production (directly decreasing the production of carbon dioxide) but it may cause better use of available resources. Both FA and GGBFS are by-products of other industrial processes and ‘‘disposing’’ them in concrete and/or masonry products is an environmentally friendly alternative to more traditional disposal methods. In the case of FA replacement, there is also a significant cost reduction. While the concept of substituting PC with pozzolans and other mineral additives is not new, the use of such materials in masonry grout is new especially at the high levels replacement presented herein. There are several benefits of increasing the substitution levels of fly ash and slag for PC in masonry grout. These benefits may include using 100% recyclable materials, making construction more affordable because less expensive materials are used; reducing their disposal in landfills, ponds, and (in many places around the world) in river systems; and making possible construction industry expansion without increasing green-house gases emission. In addition, the use of these by-product materials may make masonry concrete construction more competitive and alleviate the demand for PC especially in developing countries where masonry construction is the preferred construction method. These benefits, however, can only be realized if these materials can be used without compromising building code requirements. The building code for masonry structures [4] specifies that the compressive strength of the grout must be equal or exceed the specified compressive strength of the masonry or meet ASTM C476 [5] specifications, which requires the grout to have a minimum compressive strength of 13.8 MPa at 28 days. A comprehensive research program has been completed to determine if the minimum masonry grout strength of 13.8 MPa, obtained from testing several hundred grout specimens, could be maintained with high levels of FA and GGBFS.
2. Hydration overview The hydration of PC is complex involving the hydration of several chemical compounds that results in the formation of various products. In general terms and using oxide or shorthand notation, PC hydration involves water and five main compounds: tricalcium silicate (C3S), dicalcium silicate (C2S), tricalcium aluminate (C3A), tetracalcium aluminoferrite (C4AF), and calcium sulfate dehydrate (CSH2) [6–8]. The main hydration product of PC is a calcium silicate hydrate (C–S–H), which does not have a definite stoichiometry but whose approximate formula is C3S2H8. In addition to C–S–H, the hydration process also forms calcium hydroxide (CH), which is a compound with a definite stoichiometry, Ca(OH)2, that may make up as much as 25 percent by volume of the hydrated cement paste [6,9]. Compared with the hydration of PC alone, the hydration of PC that incorporates FA and/or GGBFS is much more complex due to the coexistence of multiple interdependent and simultaneous
reactions [10]. The hydration reaction of the two calcium silicates C3S and C2S are very similar and generates essentially the same products; the difference being in the amount produced of each compound: two C3S molecules produce three CH molecules while two C2S molecules produce one CH molecule [6–8]. The two hydration products C–S–H and CH are the basis for the effectiveness of the FA and GGBFS. Fly ash is a fine-grained particulate produced through the combustion of coal. FA is precipitated from exhaust gases by means of electrostatic attraction, is considered a waste material, and is commonly used as a pozzolanic admixture in concrete [11]. FA adds compressive strength to the concrete by means of a secondary reaction with CH [6–8,12]. In general, siliceous glass in the FA reacts with the CH to form additional C–S–H. While this secondary reaction is slower than the primary reaction involved in the hydration of PC, the small initial sacrifice in compressive strength results in increased long-term compressive strength [6–8]. Among other benefits of using FA are improved workability and increased durability [6,8]. Blast furnace slag is a by-product of the iron and steel industry. Granulated blast furnace slag is formed when molten blast furnace slag is quenched in water. Grinding reduces the particle size of the granulated blast furnace slag to the same fineness as cement, and the resulting product, ground granulated blast furnace slag (GGBFS) is typically used as a mineral admixture in cement [10,13,14]. Unlike fly ash, GGBFS will hydrate directly to form C–S–H. This process, however, is very slow unless the GGBFS is activated by an alkaline compound such as CH [6,8,14], which is fortunately formed during the PC hydration. Activation occurs because CH breaks down a relatively impervious barrier formed around the outside of the slag during the initial stages of its hydration [14]. Theoretically only between 10 to 20 percent by weight of PC is required to activate the slag [6]. Compared to mixes with no cement replacement, mixes incorporating GGBFS have improved workability and slower compressive strength development but equivalent and even higher ultimate strength. 3. High volume FA and GGBFS concrete One of the first studies of high volume substitution of PC involved concretes containing up to 50 percent of FA [15]. The observations were that those concretes had lower temperature rise due to heat of hydration, were less prone to experience thermal cracking, and had generally low compressive strength at early ages. Since that pioneering study by Davies et al. [15], a significant amount of research has been conducted on concretes containing high volumes of FA [16–24] and high volumes of GGBFS [25–29]. More specifically, in the late 1980s, the concrete research group from the materials technology laboratory at the Canada Centre for Mineral and Energy Technology (CANMET-MTL) began developing a high-volume fly ash (HVFA) concrete [30]. HVFA concrete utilizes proper mixture proportioning and careful selection of materials to minimize the amount of PC while producing high-quality concrete. HVFA concrete has low PC content (225 lb/yd3 [155 kg/m3]), low water-to-cementitious materials ratio (w/cm) (190 lb/yd3 [115 kg/m3]) and incorporates up to 60 percent FA. Because of the low w/cm, however, superplasticizers may be needed to increase workability. Over the years, CANMET-MTL, in partnership with the Electric Power Research Institute, U.S.A., Canadian Electrical Association, and other public and private partners, has published a large amount of data on the properties of HVFA concrete [31,32]. HVFA concrete has been gradually gaining acceptance [33,34] among engineers and many significant structures have been build using HVFA concrete based on CANMET’s work [35], and today, research data exist from more than 25 years of their field performance.
721
F.S. Fonseca et al. / Construction and Building Materials 94 (2015) 719–727
The proven sustainable aspects and mechanical properties benefits of incorporating high volumes of FA and GGBFS into traditional concrete are leading researchers to explore new possibilities. One of the new frontiers being explored recently is the use of high volumes of FA and BBGFS in an attempt to make self-consolidating concrete more economical [36–39]. Another possibility, which is the new research presented herein, is the use of high volumes of FA and GGBFS in masonry grout. 4. Experimental program 4.1. Phase I The objective of this phase of the project was to determine the viability of and the methodology for the overall project. In this phase, the testing regime utilized only FA as supplemental cementitious material. The mixes were proportioned by volume and, in addition to the control mix (0% FA), mixes were batched with 20%, 30%, 40%, 50% and 60% FA. The materials were Portland cement Type II complying with ASTM C150/C150M [40], coal fly ash Class F complying with ASTM C618 [41], fine aggregate (sand) complying with ASTM C404 [42], 9.5 mm aggregate (pea gravel) complying with ASTM C404 [42], and potable water. The specific gravity (SSD) of the materials were 3.15 for the Portland cement, 2.33 for the fly ash, 2.59 for the sand, and 2.59 for the pea gravel. Six batches, one per grout mix, were made, and Table 1 gives the volume (V), the unit weight (UW), and the weight (W) for each material and the free water (FW) in the sand and pea gravel. Per ASTM C476 [5], individual cementitious materials and aggregates were first measured and then mixed with a mechanical mixer for a minimum of five minutes with sufficient potable water to achieve the desired consistency. The total water to total cementitious material ratio was 0.848, 0.779, 0.854, 0.795, 0.796, 0.819 for mixes 1 through 6, respectively. Grout slump was determined according to the procedure outlined in ASTM C143/C143M [43] and was 229 mm for mixes 1 through 4, 222 mm for mix 5, and 235 mm for mix 6. The temperature of the grout was measured as prescribed by ASTM C1064/C1064M [44] and was 24.8 (22.2), 24.0 (18.7), 30.0 (23.6), 25.1 (23.3), 26.3 (24.8), and 23.2 (19.1) °C for mixes 1 through 6, respectively; the numbers in parentheses are the ambient temperature. Due to the extent of testing undertaken, an alternative method for casting the grout specimens was adopted; such a procedure is allowed by ASTM C1019 [45]. The alternative method used herein provided the absorptive mold for the grout specimen as required by ASTM C1019 [45]. A non-absorptive plastic sheet was used a barrier between the specimens and floor of the laboratory, where specimens were cast. The specimens were made by filling the hollow cores of full concrete masonry units (CMU). The specimens were prepared in two lifts and consolidated by 25 blows of a tamping rod for each lift. The specimens were finished to produce a clean level surface and were then covered with a damp cloth for 24–48 h at which point the units were moved to their storage location. Half of the specimens were wet-cured and stored in a moist room complying with ASTM C511 [46]; half of the specimens were dry-cured and stored in a dry room complying with ASTM C157 [47]. The grout samples were removed from the CMUs by saw cutting them with a diamond blade two days prior of testing; specimens were returned to their storage location immediately after the saw cutting. Three specimens for each grout mix, test age, and curing condition were made. Specimens were tested in accordance with ASTM C1019 [45] at 7, 14, 28, 42, and 56 days and were capped prior of testing with high-strength sulfur according to specification of ASTM C617 [48]. The use of an alternative method to cast the specimens necessitated that the results of the compression testing be converted to results that would have been obtained if the specimens were cast using the standard casting method [45]. Due
to the objective of this phase, which was to determine the viability of and the methodology for the overall project, the results of Phase I, however, were not converted to ‘‘standard’’ results. Results of Phase I are summarized in Table 2 and plotted in Fig. 1. For the 0%, 20%, 30%, and 40% replacement rate, the wet and dry curing methods generally yielded similar compressive strength results except for the 0% and the 20% rate at 42 days. In these two instances, the strength of specimens dry-cured were lower than that of specimens cured in wet conditions. The 0% mix did not experience an increase in strength from 28 to 42 days, which is an anomaly since strength should increase with age. Although the 20% mix experienced a small increase in strength from 28 to 42 days, the rate of strength increase from 28 to 42 days was significantly smaller than that from 42 to 56 days. The significantly different rate of strength increase can also be considered an anomaly since the rate of increase should have been more similar especially after 28 days. For the 50% and 60% replacement rate, the dry curing method yielded slightly higher strengths than the wet curing method regardless of specimen age. Theoretically, there is enough water to ensure complete hydration without additional water being supplied if a mix has a water–cement ratio of 0.42 or greater [6]. Since all mixes in Phase I had water–cement ratio significantly higher than the theoretical ratio to ensure complete hydration, all mixes should have theoretically experienced complete hydration regardless of the curing condition; in other words, curing condition should not have affected the results. The slightly higher moisture content in the wet curing environment, however, could have adversely affected the compressive strength of the 50% and 60% replacement rate specimens. Despite these small discrepancies, the wet and dry curing methods yielded very similar compressive strength results. The specimens with 20% rate replacement achieved slightly higher strengths than those made with only PC. A small decrease in early concrete strength and then an increase, which may even surpass that of specimens with only PC have been observed by others [6,7]. The results of Phase I showed the viability of using high volumes of FA in masonry grout since specimens of all replacement rates and curing conditions, except for the 60% replacement rate, reached the minimum 13.8 MPa compressive strength at the specified 28 days. 4.2. Phase II The objectives of Phase I were to determine the viability of and the methodology for the overall project. The results of Phase I show that high volume substitution of Portland cement in masonry grout is viable and it does not compromise the grout compressive strength. The results also show that the wet curing method was slightly more conservative with two exceptions at one specific testing age. In Phase II mixes were proportioned by weight, a more common practice in the United States, instead of the easier volume proportioning used in Phase I. Besides the control mix (0% FA), mixes were batched with 40%, 50% and 60% FA using the same materials as those used in Phase I. In addition, other control mix (0% FA) and three mixes with 45%, 55%, and 65% FA replacement rate were batched; these four mixes used sand and pea gravel from a different source. The new sand also complied with ASTM C404 [42] and the new pea gravel also complied with ASTM C404 [42]. The additional control mix (0% FA) was batched to directly determine the effect of different aggregates while the other three additional replacement rate mixes were batched to better define the results between the different PC replacement rates. Table 3 summarizes the weight of the materials used and free water (FW) in the sand and pea gravel. The procedure used in Phase II to make the specimens was the same as that used in Phase I; however, three variations were made between batches 1 through 4 and batches 5 thought 8. Batches 5 through 8 were batches larger than batches 1 through 4 because the grout from batches 5 through 8 was used in another
Table 1 Material for batches – Phase I. Batch 1 (0% FA)
Cement Fly ash Sand Pea gravel Water
V (m3)
UW (kg/m3)
0.030
1505.7 1153.3 1167.8 1292.7
0.091 0.060
Batch 2 (20% FA) V (m3)
UW (kg/m3)
W (kg)
105.8 78.0 34.7
2.44 1.42
0.025 0.006 0.092 0.061
1505.7 1153.3 1180.6 1307.1
37.1 7.2 108.7 80.3 30.6
FW (kg)
V (m3)
UW (kg/m3)
W (kg)
3.24 1.76
0.016 0.016 0.099 0.066
1505.7 1153.3 1148.5 1297.5
24.7 18.9 113.8 85.6 29.8
45.6
Batch 4 (40% FA)
Cement Fly ash Sand Pea gravel Water
Batch 3 (30% FA)
FW (kg)
W (kg)
FW (kg)
V (m3)
UW (kg/m3)
W (kg)
2.25 1.46
0.023 0.010 0.099 0.066
1505.7 1153.3 1215.8 1299.1
35.0 11.4 120.5 85.7 32.7
FW (kg)
V (m3)
UW (kg/m3)
W (kg)
3.35 1.84
0.013 0.020 0.099 0.066
1505.7 1153.3 1171.0 1321.5
20.0 22.9 116.0 87.2 29.9
Batch 5 (50% FA)
V (m3)
UW (kg/m3)
W (kg)
0.020 0.013 0.010 0.066
1505.7 1153.3 1211.0 1319.9
29.9 15.4 120.0 87.1 30.9
FW (kg)
5.04 1.77
Batch 6 (60% FA) FW (kg)
3.42 1.73
722
F.S. Fonseca et al. / Construction and Building Materials 94 (2015) 719–727
Table 2 Compressive strength (MPa) results of Phase I testing. Mix type
Curing condition
Curing age (days) 7
14
28
42
56
0%
Wet Dry
13.6 13.6
15.7 15.9
18.7 18.1
21.2 18.1
21.5 21.5
20%
Wet Dry
13.0 13.2
15.2 15.0
21.4 20.8
24.4 21.7
25.5 24.9
30%
Wet Dry
9.6 10.4
12.7 13.0
15.3 16.0
19.8 19.0
18.8 18.1
40%
Wet Dry
9.4 9.8
12.0 12.0
16.3 15.5
18.2 18.3
18.8 19.1
50%
Wet Dry
8.2 9.3
11.0 12.4
13.9 14.7
16.3 18.7
18.1 19.8
60%
Wet Dry
4.8 6.1
6.8 8.0
8.1 9.7
9.2 10.6
8.9 10.7
research project involving wallettes. Also, in batches 1 through 4 a target slump was used while the total water to total cementitious material ratio was let to vary; in contrast, in batches 5 through 8 a constant total water to total cementitious material ratio was used while slump was let to vary. The last variation was that batches 1 through 4 were made in open air while batches 5 through 8 were made in a controlled environment. The total water to total cementitious material ratio was 0.795, 0.735, 0.843, 0.796 for batches 1 through 4, respectively and 0.972 for batches 5 through 8, respectively. Grout slump was 235, 235, 229, 229 mm for batches 1 through 4, respectively (the target slump was 229 mm.) For batches 5 through 7, the slump was 229, 241, and 267 mm, respectively; grout from batch 8 was flowable with a slump greater than 280 mm. The temperature of the grout was 27.1 (23.6), 15.8 (16.8), 24.7 (22.9), and 17.2 (17.8) °C for mixes 1 through 4, respectively and 22.2 (20.0), 22.2 (21.1), 22.2 (20.6), and 22.1 (20.0) °C for mixes 5 through 8, respectively; the numbers in parentheses are the ambient temperature. Since the hydration reactions of PC compounds are exothermic, the measured temperature of batches 2 and 4 appear to be wrong. These two batches were made in relatively cold days and possibly the readings were switched. The same alternative method for casting the grout specimens in Phase I was adopted in Phase II; but unlike the results of Phase I, the results of Phase II were converted as specified by ASTM C1019 [45]. Whenever an alternative casting method is used, ASTM C1019 [45] requires the results from the testing of those specimens to be converted to results that would have been obtained if the specimens were cast using the standard casting method. The conversion factor is determined by dividing the average compressive strength of 12 specimens cast using the standard casting procedure by the average compressive strength of 12 specimens cast using the alternative procedure. In order to determine the conversion factor for this research project, twelve specimens were cast using the standard specimen mold and twelve specimens were cast using the alternative mold. The specimens
cast using the alternative method were removed from the CMUs by saw cutting them with a diamond blade—the same procedure used during Phase I. All 24 specimens were tested using the same procedure as that of Phase I and the average compressive strength for the two groups were calculated; the conversion factor was determined to be 1.2. The results obtained for Phase II and presented hereon have been multiplied by the 1.2 conversion factor. The results of Phase II tests for the specimens from control mix 1 (replacement rate = 0%) and control mix 5 (replacement rate = 0%,new) are summarized in Table 4. The results are plotted in Fig. 2 with a linear regression model fitted to each set of data. The slopes of the linear regression models were used to determine if compressive strength results obtained using specimens made with control mix 1 were statistically different from those obtained using specimens made with control mix 5. Since the resulting p-value was 0.053, the null hypothesis of equal means was not rejected; in other words, there was no statistically significant difference between the compressive strength of specimens made with control mix 1 and the compressive strength of specimens made with control mix 5. Thus, the compressive strength values for mix 1 and mix 5, at each curing age, are grouped together and considered as the control mix. The average compressive strength for Phase II mixes are presented in Table 5 with the number in parentheses being the standard deviation. Values are also shown in Fig. 3 with standard deviation bars; the straight lines connecting the data points are simply shown for easier identification of the data. The strength at 14 days of specimens with 50% FA is higher than that of specimens with 45% FA and just slightly lower than that of specimens with 40% FA; at 28 days, the strength of 50% FA specimens is higher than that of 40% and 45% FA specimens. Either the strength of the 50% FA specimens is too high or the strength of the 40% and 45% FA specimens is too low. Dynamic effects, if any, would have been the same for all specimens since the loading rate was the same. In addition, slenderness and end restrains effects were also similar since the geometry of the specimens was similar with minor variations. Furthermore, theoretically a specimen cannot resist more load than its capacity, which eliminates the possibility of a too high experimental measured result. Thus, the strength of the 40% and 45% FA specimens are low. While the lower strength of the 45% FA specimens could be explained partially by the different aggregates used, the lower strength of the 40% FA specimens cannot. Possible reasons for the lower strength include faulty and/or non-parallel capping, misaligned end plates, FA flocculation, or a combination thereof. The strength of 45% FA specimens after 42 days is higher than that of 40% FA specimens. The same arguments presented above are also valid for this case, indicating that most likely the strength of 40% FA specimens is low. At early ages, the data shows that both the 45% and 55% FA specimens gained strength at a greater rate than the other specimens did. After 42 days a decrease in the strength gain rate is observed for both specimen sets; the decrease for the 55% FA specimens being slightly more pronounced. The data for the 50% FA specimens have what appears to be an abnormal value at 56 days. There should be a strength gain with increasing age but the strength of the 50% FA specimens at 56 days decrease in relationship with that at 42 days. Faulty caps, misalignment of the end plates, FA flocculation, or a combination thereof may explain the discrepancy. After 56 days, the strength of the 50% FA specimens is lower than that of the 55% FA specimens, suggesting that the measured results for the 50% FA specimens may be at fault.
Fig. 1. Compressive strength of mixes 1 through 6 – Phase I.
723
F.S. Fonseca et al. / Construction and Building Materials 94 (2015) 719–727 Table 3 Material for batches – Phase II. Batch 1 (0% FA) W (kg) Cement Fly ash Sand Pea gravel Water
Batch 2 (40% FA) FM (kg)
W (kg)
49.27 150.31 63.38 35.73 Batch 5 (0% FA) W (kg)
Cement Fly ash Sand Pea gravel Water
FM (kg)
W (kg)
10.39 5.27
W (kg) 90.61 110.74 654.36 276.85 183.94
10.39 5.27
W (kg)
FM (kg)
19.68 39.43 156.76 66.12 32.07
5.30 1.18
Batch 7 (55% FA) FM (kg)
147.65 120.81 872.48 369.12 245.24
Batch 4 (60% FA) FM (kg)
18.48 18.48 155.79 65.72 24.68
2.78 0.39
Table 4 Compressive strength (MPa) for replacement rates of 0% and 0%,new. Replacement rate
W (kg)
Batch 6 (45% FA)
268.45 872.48 369.12 245.24
FM (kg)
29.59 19.68 154.58 65.24 33.04
2.56 0.89
Batch 3 (50% FA)
5.64 1.52
Batch 8 (65% FA) FM (kg)
W (kg)
FM (kg)
65.77 122.15 619.81 258.39 171.67
7.79 3.95
7.27 3.69
Table 5 Compressive strength (MPa) results of Phase II testing.
Curing age (days) 14
28
42
56
90
0%,new
25.8 20.4 27.4
28.1 25.2 25.1
25.9 34.6 29.3
35.7 31.7 30.0
35.9 39.8 34.9
0%
25.1 22.6 23.4
27.9 27.1 28.2
28.4 28.5 28.0
30.2 29.2 30.0
33.0 31.8 32.9
Age
Portland cement replacement rates 0%
40%
45%
50%
55%
60%
65%
14
24.1 (2.5) 26.9 (1.4) 29.1 (2.9) 31.2 (2.4) 34.7 (2.9)
14.7 (1.2) 18.6 (0.9) 21.0 (0.2) 22.9 (0.6) 27.6 (0.6)
10.1 (0.4) 16.0 (2.1) 23.1 (2.9) 25.9 (0.7) 34.0 (5.2)
14.4 (0.6) 19.8 (0.6) 21.6 (0.3) 20.4 (3.4) 25.1 (2.2)
8.5 (2.0) 13.2 (3.6) 19.9 (0.1) 21.0 (1.3) 26.5 (2.3)
8.0 (0.3) 9.9 (0.1) 13.3 (0.3) 14.2 (0.7) 20.2 (0.2)
4.5 (0.4) 7.1 (1.0) 12.8 (0.7) 14.1 (1.3) 19.2 (0.6)
28 42 56 90
The strength evolution of concrete can be represented by Eq. (1) [49] reasonably well.
0
0
f c ðtÞ ¼ f c28
0
t a þ bt
ð1Þ
0
where f c ðtÞ is the mean compressive strength at age t days, f c28 is the mean 28-day compressive strength, and t is the age in days. The coefficient a has units of days and the coefficient b is dimensionless, and both coefficients are determined using a regression analysis. For each grout mix, the strength results were plotted and a model was developed. From the regression analyses, the coefficients a and b as well as the coefficient of determination, R2, were determined and are summarized in Table 6. The ratio of the coefficients a and b indicates the age of the grout (in days) at which one-half of the ultimate (in time) compressive strength of the grout is reached. The coefficient of determination indicates how well the actual data fit the statistical model; in other words, it provides a measure of how well the test results are replicated by the model. The coefficient of determination varies from 0 to 1 and
the closer the value is to 1, the better the statistical model replicates the measured strengths. As shown in Table 6, all R2 values are very close to 1, which indicate that the model can represent the measured compressive strength extremely well. The strength evolution curve for each mix is shown in Fig. 4. The explanation for the observed small discrepancies in the data has been given above. The slightly differences between the data presented in Fig. 3 and the data presented in Fig. 4 is due to the numerical procedure of fitting the statistical model. The procedure sometimes ‘‘pushes’’ the curve slightly up while it sometimes ‘‘pushes’’ the curve slightly down while trying to minimize the error between the model and actual data. Mixes with PC replacement rates of 60% and 65% did not reach the minimum compressive strength at the prescribed 28 days. The compressive strengths of these mixes at 28 days are 10.44 MPa and 8.29 MPa, respectively. The mix with 60% replacement rate reached the minimum compressive strength in 44 days while the mix with replacement rate of 65% reached the minimum compressive strength in 54 days. Since the materials used in making the grout tested are variable, directly
Fig. 2. Compressive strength of mixes 1 and 5 – Phase II.
724
F.S. Fonseca et al. / Construction and Building Materials 94 (2015) 719–727
Fig. 3. Compressive strength – Phase II.
Table 6 Regression and determination coefficients. Coefficient
a (days) b R2
Mixes 0%
40%
45%
50%
55%
60%
65%
6.024 0.7452 0.9914
11.00 0.5831 0.9892
19.65 0.2535 0.9976
8.923 0.7243 0.9849
17.62 0.3 0.9923
17.59 0.3196 0.9745
19.98 0.1446 0.9873
Fig. 4. Compressive strength – Phase II.
725
F.S. Fonseca et al. / Construction and Building Materials 94 (2015) 719–727 Table 7 Material for batches – Phase III. Batch 1 (25% slag) W (kg) Cement Fly ash Slag Sand Pea gravel Water
Batch 2 (35% slag) FM (kg)
21.59 10.80 10.80 135.35 56.11 24.18
W (kg)
FM (kg)
17.24 10.80 15.10 135.22 56.02 24.27
4.60 0.90
W (kg)
12.93 10.80 19.41 134.99 55.97 24.27
Batch 4 (55% slag) FM (kg)
4.59 0.90
Batch 6 (40% slag) FM (kg)
65.77 46.98 75.17 610.73 258.39 153.15
W (kg)
4.60 0.90
Batch 5 (30% slag)
Cement Fly ash Slag Sand Pea gravel Water
Batch 3 (45% slag)
8.62 10.80 23.72 134.76 55.88 24.22
FM (kg)
4.58 0.89
Batch 7 (50% slag)
W (kg)
FM (kg)
49.32 49.33 98.66 641.27 271.31 160.81
7.27 3.69
W (kg)
W (kg)
FM (kg)
29.60 49.33 118.39 641.27 271.31 160.81
7.64 3.87
7.64 3.87
Table 8 Compressive strength (MPa) results of Phase III testing. Age
Portland cement replacement rates 0%
14 28 42 56 90
24.1 26.9 29.1 31.2 34.7
50% (2.5) (1.4) (2.9) (2.4) (2.9)
19.9 22.8 25.2 34.5 38.7
60% (2.2) (2.5) (0.3) (1.1) (0.7)
22.5 22.2 31.3 33.3 37.3
65% (1.5) (0.6) (1.9) (1.1) (0.4)
20.5 24.0 35.6 36.0 41.9
extrapolation of the data presented herein is most likely to yield slightly different results when these materials are acquired from other sources. Thus, the results presented herein should be used in conjunction with a trial batch to verify the desired or expected grout properties made with different materials. 4.3. Phase III Combinations of FA and GGBFS were used to replace PC in Phase III. The GGBFS used conformed to ASTM C989/C989M [50] specification for grade 100. Seven mixes contained both FA and GGBS were proportioned by weight and were batched with 50%, 60%, 65%, 70%, 75%, 80%, and 85% replacement rate; the amount of FA was held constant at 25% while the amount of GGBS was progressively increased. The mixes with 50, 60, 70, and 80 were made using aggregates from one source while mixes with 65, 75, and 85 were made with aggregates from a different source; the two sources are the same as those used in Phase II. Furthermore, mixes for Phase III were made at the same time as those for Phase II; thus, the 0% and 0%,new mixes discussed in Phase II were common to Phases II and III. Table 7 summarizes the weight of the materials used and free water in the sand and pea gravel. The procedure used in Phase III to make the specimens was the same as that used in Phase I with the same variations made in Phase II; i.e., batches 5 through 7 were larger batches, used a constant total water to total cementitious material ratio, and were made in a controlled environment. The total water to total cementitious material ratio was 0.688 for batches 1 through 4 even though their slump were 229, 222, 216, and 222 mm, respectively. Batch 5 through 7 had a total water to total cementitious material ratio of 0.873 while their slump were 203, 216, 267 mm, respectively. The temperature of the grout was 26.1 (28.4), 27.9 (26.2), 28.7 (27.1), and 29.1 (27.8) °C for mixes 1 through 4, respectively and 22.2 (20.0), 22.2 (20.6), 22.2 (21.1), and 22.1 (21.1) °C for mixes 5 through 7, respectively; the numbers in parentheses are the ambient temperature. Since the hydration reactions of PC compounds are exothermic, the measured temperature of batch 1 appear to be incorrect; it is possible that the reading was switched. The same alternative method for casting the grout specimens in Phases I and II was adopted in Phase III and the results were converted to results obtained from samples cast using the standard grout specimen mold using the same 1.2 conversion factor determined in Phase II. Thus, the results presented hereon for Phase III were multiplied by the 1.2 conversion factor. The average compressive strength values for the control mix and for mixes in Phase III are presented in Table 8 with the number in parentheses being the standard deviation. Values are also shown in Fig. 5 with standard deviation bars; the straight lines connecting the data points are simply shown for easier identification of the data.
70% (4.3) (1.4) (1.4) (2.3) (0.2)
19.1 23.5 29.0 29.4 32.8
75% (0.5) (1.4) (1.9) (0.7) (0.3)
20.9 19.6 27.1 29.9 33.6
80% (1.0) (2.3) (0.8) (1.6) (1.6)
13.4 16.7 18.6 21.7 23.2
85% (0.8) (2.0) (2.1) (0.2) (0.2)
11.2 13.2 16.9 19.1 20.8
(1.0) (1.4) (1.0) (0.4) (0.2)
The results for the 60 and 75FS replacement rates have at 28 days what appears to be a discrepancy since the strength decreases from that at 14 days. Faulty caps, misalignment of the end plates, FA and GGBFS flocculation, or a combination thereof may explain the discrepancy. Also noticeable is the significant increase in strength from 28 to 42 days for mixes 60, 65, and 75FS and from 42 to 56 days for mix 50FS. The strength of mixes 50 and 60FS are low compared with that of mix 65FS, which may be partially explained by the different aggregates used. The results show a large decrease in strength for mixes with 80 and 85FS replacement rate. Models were also developed to represent the strength evolution of the mixes in Phase II. The model used is given in Eq. (1) and the regression coefficients a and b as well as the coefficient of determination, R2, for each mix are summarized in Table 9. The strength evolution curve representing each mix is shown in Fig. 6. Overall, mixes with up to 75FS replacement rate have a small decrease in early strength. Strength, however, increases with time and in many cases surpasses that of the control mix. It appears that the ultimate strength of mixes with up to 75FS replacement rate will be at least as that of the control mix. Even though there is a large decrease in strength for mixes with 80 and 85FS replacement rate compared to the strength of the control mix, these mixes did reach the minimum compressive strength of 13.8 MPa at the prescribed 28 days. The ultimate strength of these mixes, however, will be most likely lower than that of the control mix.
5. Conclusions The results of the experimental research herein reported lead to the following conclusions: 1. High volume FA and FA-GGBFS replacement of PC is a viable alternative to make concrete masonry construction more economical and sustainable. 2. Grouts made with up to 55% FA and up to 85% FA-GGBFS achieve the minimum grout compressive strength of 13.8 MPa at 28 days. In other words, grouts with up to 55% class F FA and a combination of 25% class F FA and 60% GGBFS can essentially be treated as conventional masonry grout. 3. Grouts with 60% and 65% class F FA achieve the minimum grout compressive strength of 13.8 MPa at 44 and 54 days. In cases where masonry structures may not need to achieve the
726
F.S. Fonseca et al. / Construction and Building Materials 94 (2015) 719–727
Fig. 5. Compressive strength – Phase III.
Table 9 Regression and determination coefficients. Coefficient
a (days) b R2
Mixes 0%
50%
60%
65%
70%
75%
80%
85%
6.024 0.7452 0.9914
13.11 0.4636 0.9583
8.886 0.5129 0.9643
11.9 0.4426 0.9792
9.139 0.6222 0.9952
8.553 0.5136 0.9547
9.732 0.6222 0.994
10.84 0.5178 0.9888
Fig. 6. Compressive strength – Phase III.
F.S. Fonseca et al. / Construction and Building Materials 94 (2015) 719–727
minimum strength at 28 days, the results of this research provide another viable option to engineers to make concrete masonry construction more economical and sustainable. 4. Results are slightly sensitive to the aggregate used; therefore, masonry grout mix designs incorporating high volumes of supplementary cementitious materials should be evaluated and tested and the results presented herein should be used in conjunction with a trial batch to verify the desired or expected grout properties made available materials. 5. Ternary blend (PC-FA-GGBFS) grout mixes can achieve higher ultimate compressive strengths that those of binary blends (PC-FA) and PC only grout mixes. Acknowledgements This testing program would not have been possible without the support of the following people and organizations: Paul Jahn from Ash Grove Packaging; David Anderson, Rodney Mayo, and David Wilson from BYU; Rick Child from Child Enterprises; Kevin Hatfield from Doyle Hatfield Masonry; Jim Johnson and Chris Bedford from Headwaters; Heath Holdaway from IMS Masonry; Rob Shogren and Todd Sherman from Lafarge; Dennis W. Graber, Nick Lang, Bob Thomas and Jason Thompson from National Concrete Masonry Association; Wade Ficklin, Paul Kamnikar and Gerald Travis from Oldcastle; Scott Hanks and Tyler Clark from Quikrete, and Brent Overson from Utah Masonry Council. The following BYU students helped during construction of the hundreds of specimens: Jacob Ballard, Zifan Guo, Juan Manuel Salguero Mendizabel, Brice Somers, and Scott Watterson. These students were supported financially by a generous Grant from the NCMA Education and Research Foundation. References [1] Hanle, L.J.; Jayaraman, K.R.; and Smith, J.S., CO2 Emissions Profile of the U.S. Cement Industry, http://www.epa.gov/ttn/chief/conference/ei13/index.html, 13th International Emission Inventory Conference, Florida, USA, June 8–10, 2004. [2] F. Hogan, J. Meusel, L. Spellman, Breathing Easier With Blast Furnace Slag, Rock Products, Cement Americas (2001) 11–15. [3] Chesner, W.; Collins, R.; and MacKay, M., User Guidelines for Byproduct and Secondary Use Materials in Pavement Construction, U.S. Dept. of Transportation, Federal Highway Administration, Research and Development, Turner-Fairbank Highway Research Center, Available to the public through the National Technical Information Service in McLean, VA, Publication Number: FHWA-RD-97-148, April, 1998. [4] Masonry Standards Joint Committee, Building Code Requirements for Masonry Structures (TMS 402-11/ACI 530-11/ASCE 5-11). The Masonry Society, Boulder, CO; America Concrete Institute, Farmington Hills, MI; Structural Engineering Institute of the America Society of Civil Engineers, Reston, VA. [5] ASTM C476-10, Standard Specification for Grout for Masonry, ASTM International, West Conshohocken, PA, 2010. [6] S. Mindess, J.F. Young, D. Darwin, Concrete, Second ed., Pearson Education Inc., Upper Saddle River, NJ, USA, 2003. [7] A.M. Neville, Properties of Concrete, Fourth and Final ed., Pearson Education Limited, Edinburgh Gate, Harlow, Essex CM20 2JE, England, 1995. [8] P.K. Mehta, P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials, Third ed., The McGraw-Hill Companies Inc., Two Penn Plaza, New York, NY, 2006. [9] Q. Zeng, K. Li, T. Fen-chong, P. Dangla, Determination of cement hydration and pozzolanic reaction extents for fly-ash cement pastes, Constr. Build. Mater. 27 (1) (2012) 560–569. [10] X.Y. Wang, H.S. Lee, Modeling the hydration of concrete incorporating fly ash or slag, Cem. Concr. Res. 40 (7) (2010) 984–996. [11] R. Helmut, Fly Ash in Cement and Concrete, Portland Cement Association, Skokie, IL, 1987. [12] Y.M. Zhang, W. Sun, H.D. Yan, Hydration of high-volume fly ash cement pastes, Cement Concr. Compos. 22 (6) (2000) 445–452. [13] S.C. Pal, A. Mukherjee, S.R. Pathak, Investigation of hydraulic activity of ground granulated blast furnace slag in concrete, Cem. Concr. Res. 33 (9) (2003) 1481–1486. [14] S. Song, D. Sohn, H.M. Jennings, T.O. Mason, Hydration of alkali-activated ground granulated blast furnace slag, J. Mater. Sci. 35 (1) (2000) 249–257. [15] R.E. Davis, R.W. Carlson, J.W. Kelly, H.E. Davis, Properties of cements and concretes containing fly ash, ACI J. Proc. 33 (5) (1937) 577–612. [16] M.R.H. Dunstan, Development of high fly ash content concrete, ICE Proc. 74 (3) (1983) 577–611.
727
[17] M.N. Haque, M.K. Goplan, R.C. Joshi, M.A. Ward, Strength development of inadequately cured high fly ash content and structural concretes, Cem. Concr. Res. 16 (3) (1986) 363–372. [18] D. Ravina, P.K. Mehta, Compressive strength of low cement/high fly ash concrete, Cem. Concr. Res. 18 (4) (1988) 571–583. [19] A. Bilodeau, V.M. Malhotra, High-volume fly ash system: concrete solution for sustainable development, ACI Mater. J. 97 (1) (2000) 41–48. [20] A. Bisaillon, M. Rivest, V.M. Malhotra, Performance of high-volume fly ash concrete in large experimental monoliths, ACI Mater. J. 91 (2) (1994) 178–187. [21] W.S. Langley, G.G. Carette, V.M. Malhotra, Structural concrete incorporating high volumes of ASTM class fly ash, ACI Mater. J. 86 (5) (1989) 507–514. [22] T.R. Naik, B.W. Ramme, Low cement content high strength concrete, Cem. Concr. Res. 17 (2) (1987) 283–294. [23] T.R. Naik, B.W. Ramme, High-strength concrete containing large quantities of fly ash, ACI Mater. J. 86 (2) (1989) 111–116. [24] D. Ravina, P.K. Mehta, Properties of fresh concrete containing large amounts of fly ash, Cem. Concr. Res. 16 (2) (1986) 227–238. [25] V. Sivasundarum, V.M. Malhotra, Properties of concrete incorporating low quantity of cement and high volumes of ground granulated slag, ACI Mater. J. 89 (6) (1992) 554–563. [26] T. Tomisawa, M. Fujii, Effects of high fineness and large amounts of ground granulated blast-furnace slag on properties and microstructure of slag cement, in: V.M. Malhotra (Ed.), Fly Ash, Silica Fume, Slag and Natural Pozzolans in Concrete, SP 153, American Concrete Institute, Farmington Hills, Michigan, 1995, pp. 951–971. [27] M. Elchalakani, T. Aly, E. Abu-Aisheh, Sustainable concrete with high volume GGBFS to build Masdar City in the UAE, Case Stud. Constr. Mater. 1 (2014) 10–24. [28] Richardson, D.N., Strength and durability characteristics of a 70% ground granulated blast furnace slag (GGBFS) concrete mix, Final Report RI99-035/ RI99-035B, Missouri Department of Transportation, February 2006. [29] Anderson, K.W.; Uhlmeyer, J.S.; Williams, K., Russell, M., Evaluation of portland cement concrete pavement with high slag content cement, Final Report WARD 728.2, Washington State Department of Transportation, October 2013. [30] American Concrete Institute Committee 232, Report on High-Volume Fly Ash Concrete For Structural Applications, ACI 232.3R-14, American Concrete Institute, Farmington Hills, MI, October 2014. [31] V.M. Malhotra, High-performance high-volume fly ash concrete, Concr. Int. 24 (7) (2002) 30–34. [32] N. Bouzoubaa, V.M. Malhotra, Performance of lab-produced high-volume fly ash cements in concrete, Concr. Int. 23 (4) (2001) 29–33. [33] D. Manmohan, P.K. Mehta, Heavily reinforced shearwalls and mass foundations built with ‘green’ concrete, Concr. Int. 24 (8) (2002) 64–70. [34] D. Cross, J. Stephens, J. Vollmer, Field trials of 100% fly ash concrete, Concr. Int. 27 (9) (2005) 47–51. [35] V.M. Malhotra, P.K. Mehta, High-performance, High-Volume Fly Ash Concrete for Building Sustainable and Durable Structures, Third ed., Supplementary Cementing Materials for Sustainable Development, Inc., Ottawa, Canada, 2008. [36] N. Bouzoubaâ, M. Lachemi, Self-compacting concrete incorporating high volumes of class F fly ash: preliminary results, Cem. Concr. Res. 31 (3) (2001) 413–420. [37] T.R. Naik, R. Kumar, B.W. Ramme, F. Canpolat, Development of high-strength, economical self-consolidating concrete, Constr. Build. Mater. 30 (2012) 463– 469. [38] G. Hannesson, K. Kuder, R. Shogren, D. Lehman, The influence of high volume of fly ash and slag on the compressive strength of self-consolidating concrete, Constr. Build. Mater. 30 (2012) 161–168. [39] K. Kuder, D. Lehman, J. Berman, G. Hannesson, R. Shogren, Mechanical properties of self consolidating concrete blended with high volumes of fly ash and slag, Constr. Build. Mater. 34 (2012) 285–295. [40] ASTM C150/C150M-12, Standard Specification for Portland Cement, ASTM International, West Conshohocken, PA, 2012. [41] ASTM C618-08, Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete, ASTM International, West Conshohocken, PA, 2008. [42] ASTM C404-11, Standard Specification for Aggregates for Masonry Grout, ASTM International, West Conshohocken, PA, 2011. [43] ASTM C143/C143M-12, Standard Test Method for Slump of Hydraulic-Cement Concrete, ASTM International, West Conshohocken, PA, 2012. [44] ASTM C1064/C1064M-12, Standard Test Method for Temperature of Freshly Mixed Hydraulic-Cement Concrete, ASTM International, West Conshohocken, PA, 2012. [45] ASTM C1019-13, Standard Test Method for Sampling and Testing Grout, ASTM International, West Conshohocken, PA, 2013. [46] ASTM C511-13, Standard Specification for Mixing Rooms, Moist Cabinets, Moist Rooms, and Water Storage Tanks Used in the Testing of Hydraulic Cements and Concretes, ASTM International, West Conshohocken, PA, 2013. [47] ASTM C157/C157M-08, Standard Test Method for Length Change of Hardened Hydraulic-Cement Mortar and Concrete, ASTM International, West Conshohocken, PA, 2008. [48] ASTM C617/C617M-11, Standard Practice for Capping Cylindrical Concrete Specimens, ASTM International, West Conshohocken, PA, 2011. [49] ACI 209.2R-08, Guide for Modeling and Calculating Shrinkage and Creep in Hardened Concrete, Reported by ACI Committee 209, American Concrete Institute, Farmington Hills, MI, 2008. [50] ASTM C989/C989M-14, Standard Specification for Slag Cement for Use in Concrete and Mortars, ASTM International, West Conshohocken, PA, 2014.