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Effect of types of aggregate and sand-to-aggregate volume ratio on UPV in concrete
Construction and Building Materials 125 (2016) 832–841
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Effect of types of aggregate and sand-to-aggregate volume ratio on UPV in concrete Tarek Uddin Mohammed, Md Nafiur Rahman ⇑ Department of Civil and Environmental Engineering, Islamic University of Technology (IUT), Board Bazar, Gazipur 1704, Bangladesh
h i g h l i g h t s Variation of UPV in concrete with types of aggregates and s/a. Four different types of aggregate were investigated. s/a ratios were 0.36, 0.40, and 0.44. UPV in concrete significantly influenced by the types of aggregate and s/a. With the increase of s/a, UPV in concrete is reduced.
a r t i c l e
i n f o
Article history: Received 27 April 2016 Received in revised form 6 July 2016 Accepted 25 August 2016
Keywords: Brick chips Compressive strength Modulus of elasticity Sand to aggregate volume ratio UPV
a b s t r a c t An experimental investigation was carried out to understand the variation of ultrasonic pulse velocity (UPV) in concrete with the types of coarse aggregate and sand-to-aggregate volume ratio (s/a). The types of aggregate investigated were brick chips, crushed stone, round shaped stone and black stone. Sand-toaggregate ratios were 0.36, 0.40, and 0.44 and W/C ratios were 0.45, 0.50, and 0.55. Concrete specimens were made and tested for UPV, compressive strength, and modulus of elasticity. UPV in concrete is significantly influenced by the types of aggregate and s/a ratio in addition to the compressive strength of concrete. UPV in concrete is reduced with the increase of s/a ratio. Relationships between UPV and compressive strength, and UPV and modulus of elasticity are proposed for aggregates investigated. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction From the viewpoint of structural health evaluation of concrete structures, ultrasonic pulse velocity (UPV) in concrete has been found to be an important parameter. Many investigations were carried out to understand the variation of UPV with compressive strength of concrete [1–7]. To establish the correlations between UPV and compressive strength, different studies were carried out with the variation of types of aggregate [1,8–10], maximum size of aggregate [11–14], different grades of recycled aggregates [15,16], absorption [17], age [1,2,18,19], workability [20], W/C [2,21], and porosity of concrete [22]. It had been established that similar to compressive strength, UPV of concrete also develops with age and it is inversely proportional with volume of pores in concrete [15]. Rate of change of UPV in concrete with time can be used not only to determine the setting of concrete but also to ⇑ Corresponding author. E-mail addresses: [email protected] (T.U. Mohammed), [email protected] (M.N. Rahman). http://dx.doi.org/10.1016/j.conbuildmat.2016.08.102 0950-0618/Ó 2016 Elsevier Ltd. All rights reserved.
indicate different stages of microstructural changes at early ages of concrete [23,24]. It had been also found that UPV is affected by the microstructural variations in mortar and can be used to estimate sand content in mortar effectively [25]. UPV of concrete was also studied to detect damage inside the concrete [26–28]. Also evaluations of UPV for different types of concrete like lightweight or asphalt concrete were also conducted [29,30]. Recently, different types of statistical approach had been taken to predict compressive strength of concrete from UPV using Principle Component Analysis (PCA) and Artificial Neural Network (ANN) where compressive strength can be predicted for a variety of mix proportions and types of aggregate with a relatively smaller margin of error [8,25]. Structural health of RC structures was also evaluated by UPV [31]. Although many researchers carried out detailed investigations to understand how UPV of concrete varies with compressive strength, very limited number of literatures were found where sand-to-aggregate (s/a) volume ratio was considered as a governing parameter. As sand-to-aggregate (s/a) volume ratio has a significant influence on compressive strength of concrete,
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therefore, it is necessary to investigate how UPV of concrete varies with s/a ratios. It can be noted that s/a of existing concrete structures can be estimated based on the mix design of concrete or cut section of a structural element. For accurate estimation of compressive strength from UPV, s/a ratio is to be carefully determined. Previous studies confirm that variation of UPV in concrete made with different types of aggregate primarily accounts for two important variables, one is the acoustic impedance property and another is the quality of the aggregates [17,32]. In Bangladesh, some detailed investigations were carried out to understand the mechanical behavior of concrete made with different types of aggregates including recycled aggregates [33–35]. Studies are still necessary to correlate compressive strength with UPV for concrete made with different aggregates. Recently in Bangladesh, after the collapse of a garments factory that killed more than 3000 workers, it becomes an important task to the civil engineers to assess the safety of the existing structures. For safety assessment, evaluation of compressive strength of concrete is an important requirement. Determination of compressive strength by cutting core is not an easy method. Also, cutting cores from columns may hamper the load carrying capacity of the columns. On the other hand, UPV through concrete can be evaluated easily for different structural elements. Most of the RC structures in Bangladesh are made of brick aggregates due to lack of availability of stone aggregates. Sometimes crushed stone, round shaped stone aggregate (locally known as shingles) and black stone (extracted from quarry) are also used. Therefore, it is necessary to make a comprehensive study on the effect of different types of aggregate on UPV of concrete. As s/a ratio may change depending on mixture proportions of concrete,
Round Shaped Stone
therefore investigations on the variation of UPV with s/a are necessary. With the above-mentioned background, a detailed experimental investigation was carried out by varying types of aggregate, s/ a, and W/C. UPV in concrete made with different types of aggregate is compared and several relationships are proposed for evaluation of compressive strength, and modulus of elasticity of concrete from UPV. The results will be very useful for evaluation of structural health of existing concrete structures.
2. Experimental method 2.1. Materials Coarse aggregates investigated in this study include brick chips, crushed stone, round shaped stone, and black stone as shown in Fig. 1. Natural river sand was used as fine aggregate. The aggregates were tested for specific gravity, absorption capacity, fineness modulus, and abrasion according to ASTM specifications. The chemical compositions (determined using X-ray Fluorescence (XRF) Spectroscopy) and physical properties of coarse aggregates are summarized in Tables 1 and 2 respectively. The maximum size of coarse aggregate was 19 mm. The grading of aggregates was controlled as per the requirement of ASTM C33 as shown in Fig. 2. The specific gravity (SSD), absorption capacity, fineness modulus and unit weight of fine aggregate were 2.45, 3.30%, 2.52 and 1520 kg/m3 respectively. CEM type II/A-M (as per BDS EN 197–1:2000) was used which consists of 80–94% clinker and 6–20% of mineral admixture and gypsum.
Crushed Stone
Black Stone
Brick Chips Fig. 1. Coarse aggregates investigated in this study.
Table 1 Chemical compositions of coarse aggregates investigated. Oxides (% by weight)
CaO
SiO2
Al2O3
Fe2O3
MgO
Na2O
K2O
Others
Brick chips (BC) Crushed stone (CS) Round shaped stone (SG) Black stone (BS)
8.67 1.25 – 12.56
53.42 88.23 74.12 58.35
15.29 0.14 3.78 11.41
8.24 0.84 0.61 11.39
4.06 0.27 0.73 1.80
0.83 0.51 – 0.21
0.24 0.29 – 0.02
9.25 8.47 20.76 4.26
Table 2 Physical properties of coarse aggregates investigated. Type of coarse aggregate
Fineness modulus (FM)
% Wear
Bulk specific gravity in SSD condition
Absorption capacity (%)
Unit weight (kg/m3)
Brick chips (BC) Crushed stone (CS) Round shaped stone (SG) Black stone (BS)
Controlled as per ASTM C33
38.26 38.76 27.3 10.9
2.30 2.56 2.58 2.84
15.06 2.39 1.16 1.45
1236 1549 1671 1836
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Fig. 2. Grading of coarse aggregate (Left) and fine aggregate (Right).
2.2. Mixture proportion and specimen preparation For this study, 100 mm 200 mm cylindrical concrete specimens were made with sand to aggregate (s/a) volume ratios of 0.36, 0.40, and 0.44. s/a is defined as the ratio of absolute volume of fine aggregate to absolute volume of coarse and fine aggregate
per unit volume of concrete. Water to cement (W/C) ratios were 0.45, 0.50, and 0.55. The specimens were made for different types of coarse aggregate such as brick chips (BC), crushed stone (CS), round shaped stone (SG), and black stone (BS). The mixture proportions for all cases investigated are summarized in Table 3. As summarized in Table 3, for each type of aggregate nine different
Table 3 Mixture proportions of concrete. Type of aggregate
Notation of case
Brick chips
BC-45-36-395 BC-50-36-372 BC-55-36-351 BC-45-40-395 BC-50-40-372 BC-55-40-351 BC-45-44-395 BC-50-44-372 BC-55-44-351 CS-45-36-395 CS-50-36-372 CS-55-36-351 CS-45-40-395 CS-50-40-372 CS-55-40-351 CS-45-44-395 CS-50-44-372 CS-55-44-351 SG-45-36-395 SG-50-36-372 SG-55-36-351 SG-45-40-395 SG-50-40-372 SG-55-40-351 SG-45-44-395 SG-50-44-372 SG-55-44-351 BS-45-36-395 BS-50-36-372 BS-45-40-395 BS-50-40-372 BS-45-44-395 BS-50-44-372
Crushed stone
Round shaped stone
Black stone
W/C
0.45 0.50 0.55 0.45 0.50 0.55 0.45 0.50 0.55 0.45 0.50 0.55 0.45 0.50 0.55 0.45 0.50 0.55 0.45 0.50 0.55 0.45 0.50 0.55 0.45 0.50 0.55 0.45 0.50 0.45 0.50 0.45 0.50
s/a
0.36
0.40
0.44
0.36
0.40
0.44
0.36
0.40
0.44
0.36 0.40 0.44
Cement paste (%)
Mixture proportion, kg/m3 Cement
Water
Fine aggregate
Coarse aggregate
32
395 372 351 395 372 351 395 372 351 395 372 351 395 372 351 395 372 351 395 372 351 395 372 351 395 372 351 395 372 395 372 395 372
178 186 193 178 186 193 178 186 193 178 186 193 178 186 193 178 186 193 178 186 193 178 186 193 178 186 193 178 186 178 186 178 186
588
980
652
919
718
857
588
1091
652
1023
718
955
588
1110
652
1031
718
962
588
1211
652
1135
718
1059
Unit weight of fresh concrete (kg/m3)
28-Day compressive strength (MPa)
2141 2126 2112 2144 2129 2115 2148 2133 2119 2252 2237 2223 2248 2233 2219 2246 2231 2217 2271 2256 2242 2256 2241 2227 2253 2238 2224 2372 2357 2360 2345 2350 2335
17.3 15.9 14.9 23.1 17.3 16.7 26.7 21.5 20.3 25.5 19.6 17.9 27.2 22.5 20.9 30.7 24.7 23.7 23.2 18.2 16.8 25.5 20.5 19.2 28.4 22.4 21.2 26.4 22.7 30.4 27.5 33.2 25.6
Explanation of notations – the first two alphabets indicate type of aggregate (for brick chips-BC, crushed stone-CS, round shaped stone-SG, and black stone-BS), second two digits indicate W/C, third two digits indicate sand to total aggregate (s/a) ratio in %, and the last three digits indicate cement content in kg/m3. W/C – water-to-cement ratio; s/ a – sand to total aggregate volume ratio.
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cases were investigated. The number of cases investigated for black stone aggregate was six. The volume of cement paste content was kept constant at 32% i.e. 32% of total volume of concrete is filled with cement and water. Altogether 408 concrete specimens were made for 33 different cases. Unit weight of fresh concrete and 28-day compressive strength are also summarized in Table 3. In the mix proportions, cement and water contents were adjusted with the change of W/C to fix the volume of cement paste at 32%. Irrespective of types of coarse aggregate being investigated, the absolute volume of coarse aggregate (VCA) and fine aggregate (VFA) were kept constant for each s/a ratio. So the fine aggregate content is kept same for different types of coarse aggregate but coarse aggregate contents is changed based on the specific gravity of the type of coarse aggregate. The volume of cement paste is defined as:
Cement Paste ð%Þ ¼
100 ðV c þ V w Þ ðV c þ V w þ V CA þ V FA Þ
ð1Þ
where Vc = Absolute volume of cement, Vw = Volume of water, VCA = Absolute volume of coarse aggregate, and VFA = Absolute volume of fine aggregate per unit volume of concrete. Concrete specimens were casted in steel molds and kept under a humid environment for 24 h. The specimens were demolded after 24 h of casting and kept in underwater till the age of testing.
Prior to compressive strength test, concrete specimens were tested for ultrasonic pulse velocity (UPV) as per ASTM C597 by using Portable Ultrasonic Non-destructive Digital Indicating Tester (PUNDIT). The transducers of the pulse meter were held firmly along the length of the concrete specimen. Castrol Pyroplex Blue grease was used as couplant to ensure full contact between the transducers and the specimen. The time required by the pulse to travel from transmitting end to the receiver end of transducers was recorded for determination of UPV. For each cylindrical specimen, UPV along the axis of the specimen was measured three times and the average value was used for discussion. Nominal frequency of the ultrasonic pulse meter was 54 kHz. A photograph of measurement of UPV in concrete is shown in Fig. 3. The concrete specimens are also tested for compressive strength as per ASTM C39, and modulus of elasticity of concrete at the ages of 7, 28, 60, and 90 days. Modulus of elasticity was determined from stress-strain curve of concrete. The modulus of elasticity was determined by dividing compressive stress at strain level 0.0005. Tests for black stone aggregate were carried out at 28 days only due to limited number of specimens. 3. Results and discussions 3.1. Influence of types of aggregate on UPV The variation of UPV and compressive strength of concrete made with brick chips, crushed stone, round shaped stone, and black stone at the age of 28 days are shown in Figs. 4 and 5 respectively. The ranges of UPV and compressive strength of concrete for different aggregates are summarized in Table 4. The lowest UPV and compressive strength are found for concrete made with brick aggregate where the highest UPV and compressive strength are found for concrete made with black stone. As summarized in experimental method (Table 2), brick chips had the highest absorption capacity, lowest specific gravity and unit weight among the other coarse aggregates investigated. Coarse aggregate with high absorption capacity contains a lot of pores. These pores reduce UPV as it tries to pass through the concrete specimens. It is understood that aggregate with higher absorption capacity and less unit weight contributes to lesser UPV in concrete.
Fig. 3. Measurement of UPV through concrete.
Brick Chips
2.3. Testing of specimens
Crushed Stone
Round Shaped stone
Fig. 4. UPV of concrete made with different types of aggregate at 28 days.
Black Stone
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Fig. 5. Compressive strength of concrete made with different types of aggregate at 28 days.
Table 4 Range of UPV of concrete made with different types of aggregate. Type of aggregate
Compressive strength (MPa)
UPV through concrete (m/s)
Brick chips (BC) Crushed stone (CS) Round shaped stone (SG) Black stone (BS)
14.7–26.7 17.4–30.7 16.7–28.4 22.7–33.2
3290–3660 4273–4395 4326–4601 4610–4731
In case of black stone, the lowest wear value (Table 2) indicates that it was the strongest among the aggregate investigated in this study. Also, it had shown the highest specific gravity and unit weight among the other aggregates implying that the aggregate was relatively dense. The denser and stronger physical property of the aggregate allowed UPV to travel faster in concrete made with black stone and also gives the highest strength compared to similar cases of coarse aggregates investigated. UPV of concrete made with round shaped stone is slightly better compared to UPV of concrete made with crushed stone. This is because the round shaped stone can be judged as relatively stronger and denser
compared to crushed stone based on the results of specific gravity and wear value (Table 2). As a result, the ultrasonic pulse travels faster in concrete made with round shaped stone. But round shaped stone gives lower compressive strength, which is expected due to less interlocking of the aggregate and relatively poor quality of interfacial transition zone (ITZ) [36]. It is observed that irrespective of the types of aggregate, compressive strength and UPV of concrete are reduced with the increase of W/C. It is also noted that with the increase of s/a, compressive strength is increased but UPV is reduced. It is clear that UPV varies with types of aggregate being investigated. Thus it is difficult to establish a generalized relationship between compressive strength of concrete and UPV without considering the type of aggregate used in concrete. UPV in concrete with respect to type of aggregates can be ordered as black stone > round shaped stone > crushed stone > brick chips for similar level of strength. 3.2. Influence of age on UPV The variations of UPV and compressive strength with age are shown in Fig. 6. Irrespective of the types of aggregate, UPV is increased with time due to the development of strength of
Round Shaped Stone Crushed Stone Brick Chips
Fig. 6. Development of UPV and compressive strength with age of concrete.
T.U. Mohammed, M.N. Rahman / Construction and Building Materials 125 (2016) 832–841
concrete for continuous hydration of cement. It is found that concrete made with crushed stone shows higher compressive strength than concrete made with round shaped stone aggregate. But UPV is found to be higher for concrete made with round shaped stone aggregate compared to crushed stone. It is because of better physical properties of round shaped aggregate, such as lower absorption capacity and relatively lower wear value (Table 2). On the other hand, relatively higher compressive strength for concrete made with stone chips can be explained due to better aggregate interlocking due to its angularity and also formation of an improved interfacial transition (ITZ) zone around the aggregate compared to smooth and round shaped aggregate [36]. The rate of increase of UPV at early age is higher for concrete made with round shaped stone and crushed stone compared to brick chips. The rate of increase of UPV with time for brick chips is lower compared to the other aggregates. Variation of compressive strength and UPV with time for black stone aggregate is not included here as the aggregate was tested at 28-day only. Based on the data of 28-day, it is understood that concrete made with black stone will give higher compressive strength of concrete compared to concrete made with other coarse aggregates due to the better physical properties of aggregate as summarized in Table 2.
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3.3. Influence of s/a on UPV The variations of compressive strength of concrete with UPV for different types of aggregates and different s/a ratios are shown in Fig. 7. Due to limited number of data for black stone, the lines are not shown for this type of aggregate. It is observed that for a given compressive strength, concrete made with round shaped stone shows the highest UPV. Concrete made with crushed stone shows comparatively lower UPV. The lowest UPV is observed for concrete made with brick chips. Similar trend of results is obtained for all s/a ratios. It is also observed that at 28-day, black stone shows similar UPV to round shaped stone. The results prove that irrespective of s/a ratio, the type of aggregate has significant influence on UPV in concrete. Same as the previous sections, ultrasonic pulse velocity of concrete with respect to type of aggregate can be ordered as black stone > round shaped stone > crushed stone > brick chips. To investigate how the pulse velocity of concrete made with same type of aggregate varies with different s/a ratios, compressive strength is plotted against UPV in concrete made with brick chips, crushed stone, and round shaped stone as shown in Fig. 8. It is observed that irrespective of type of aggregate,
Fig. 7. Compressive strength vs pulse velocity for different types of aggregate with respect to s/a ratio.
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To explain the results with further details, compressive strength and UPV in concrete made with different types of aggregate are plotted for each s/a ratio for W/C of 0.55 and cement content of 351 kg/m3 as shown in Fig. 9. It is observed that with the increase of s/a ratio, compressive strength of concrete is increased irrespective of type of aggregate but pulse velocity of concrete is reduced. The increase in s/a ratio (from 0.36 to 0.44) results in better compaction of concrete that gives more compressive strength of concrete. Again, with the increase of s/a ratio, coarse aggregate content in concrete is reduced, therefore UPV is reduced. It is clearly understood that in order to predict compressive strength of concrete from UPV with reasonable accuracy, s/a ratio should be considered as a governing parameter in addition to the types of aggregate. 3.4. Relationships between compressive strength and UPV with the variation of s/a Based on Fig. 8, relationships were developed between 0 compressive strength (f c) and UPV in concrete for different aggregates with the variation of s/a. The results are summarized in Table 5. The exponential relationships of Table 5 can be expressed in the following generalized form: 0
f c ¼ A eBUPV
ð11Þ
where ‘‘A” and ‘‘B” are coefficients of the exponential equation. ‘A’ indicates the position of exponential lines from the axis of compressive strength. The more is the values of ‘A’, the more is the shifting of graphs from the axis of compressive strength. From the exponential relationships, it is found that the value of ‘A’ is different for different types of aggregate (highest for crushed stone then round shaped stone then brick aggregate). Also, the value of ‘A’ is decreased with the increase of s/a. Coefficient ‘B’ indicates the rate of change of compressive strength with UPV. Interestingly, it is noted that for a particular type of aggregate, the value of ‘B’ is almost constant irrespective of s/a. Based on this observation, compressive strength and UPV in concrete can be represented by the following relationships for different aggregates investigated: 0
f c ¼ K A eBUPV
ð12Þ
where ‘K’ is a factor related to s/a ratio. The values of A, B, and K are summarized in Table 6. 3.5. Relationships between modulus of elasticity and UPV
Fig. 8. Compressive strength vs pulse velocity of concrete.
pulse velocity of concrete varies with s/a ratio. The lines move rightward in parallel with the decrease of s/a. It is clearly observed that for the same strength of concrete, UPV is reduced with the increase of s/a. It is also understood that an exponential relationship between compressive strength and UPV can be formed for each type of aggregate with an inclusion of a factor related to s/a. From Fig. 7, it is also found that the compressive strength versus UPV lines are not parallel for different aggregates. Therefore, a general exponential equation cannot be formed between UPV and compressive strength for all aggregates. The relationships between UPV and compressive strength are explained in the next section.
An attempt was also made to correlate compressive strength of concrete with squared value of UPV. Similar type of relationships are also proposed by other researchers [14]. The results are shown in Fig. 10. It is found that for each type of aggregate, the lines move rightward in parallel with the decrease of s/a. Exponential relationships are developed between modulus of elasticity and UPV2 for different aggregates and different s/a. The results are summarized in Table 7. Even though the data are dispersed, but an attempt has been made to derive a simple relationship that can be used for prediction of compressive strength and Young’s Modulus from UPV. Similar level of dispersions of data can also be found in other literature [4,5,11,37]. The exponential relationships between modulus of elasticity (Ec ) and UPV can be expressed by the following equation:
Ec ¼ A eBUPV
2
ð22Þ
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Fig. 9. Effect of s/a ratio on strength and UPV (W/C – 0.55 and Cement content – 351 kg/m3). Table 5 Relationships between compressive strength and UPV of concrete for different aggregates with the variation of s/a. Types of aggregate
s/a
R2 value
Equation number
0
0.82 0.73 0.51
(2) (3) (4)
0
0.74 0.75 0.81
(5) (6) (7)
0
0.79 0.93 0.91
(8) (9) (10)
Relationship between UPV and compressive strength
Brick chips
0.36 0.40 0.44
fc ¼ 0:8944e0:00080UPV 0 fc ¼ 0:3599e0:00115UPV 0 fc ¼ 0:1662e0:00140UPV
Crushed stone
0.36 0.40 0.44
fc ¼ 1:2277e0:000660UPV 0 fc ¼ 1:2003e0:000680UPV 0 fc ¼ 1:1502e0:00070UPV
Round-shaped stone
0.36 0.40 0.44
fc ¼ 0:5836e0:00080UPV 0 fc ¼ 0:5201e0:00085UPV 0 fc ¼ 0:4719e0:00090UPV
Table 6 0 Values of A, B, and K for exponential relationships between f c and UPV. Types of Aggregate
s/a
Values of A, B and K A
B
K
Brick chips
0.44 0.40 0.36
0.1662
0.0014
1 0.922 0.685
Stone chips
0.44 0.40 0.36
1.1502
0.0007
1 0.969 0927
Round shaped stone
0.44 0.40 0.36
0.471
0.0009
1 0.922 0.871
840
T.U. Mohammed, M.N. Rahman / Construction and Building Materials 125 (2016) 832–841 Table 8 Values of A, B, and K for relationships between Ec and UPV2. Types of aggregate
s/a
Values of A, B and K A
B
K
Brick chips
0.44 0.40 0.36
10425
0.0672
1 0.919 0.765
Stone chips
0.44 0.40 0.36
9394
0.0514
1 0.913 0.854
Round shaped stone
0.44 0.40 0.36
12379
0.032
1 0.941 0.799
value of ‘A’ is increased with the increase of s/a. It is also found that the value of ‘B’ is almost constant for a particular type of aggregate irrespective of s/a. The relationship can be further generalized in the following form:
Ec ¼ K A eBUPV
2
ð23Þ
where ‘K’ is a factor related to s/a. The values of A, B, and K are summarized in Table 8. 4. Conclusions From the scope of this investigation, the following conclusions are drawn: UPV in concrete is strongly influenced by the types of aggregate and s/a ratio. UPV of concrete can be ordered as black stone > round shaped stone > crushed stone > brick chips for the same strength of concrete. With the increase of s/a ratio, UPV of concrete is reduced. Exponential relationships are proposed between compressive strength of concrete and UPV for different aggregates with incorporation of a factor related to s/a ratio. Exponential relationships are proposed between modulus of elasticity of concrete and squared values of UPV for different aggregates with incorporation of a factor related to s/a ratio.
Acknowledgments Fig. 10. Relationship between modulus of elasticity and UPV.
From the exponential relationships, it is found that the value of ‘A’ is different for different types of aggregate (highest for round shaped stone then crushed stone then brick aggregate). Also, the
The authors acknowledge the financial support and facilities provided by Islamic University of Technology (IUT) for research works in the field of concrete technology at the Department of Civil and Environmental Engineering (CEE). The authors also wish to express their gratitude to Seven Circle Bangladesh Ltd. for providing materials for this study.
Table 7 Relationships between Young’s modulus and UPV of concrete for different aggregates with the variation of s/a. R2 value
Equation number
0:1459UPV
2
0.66
(13)
Ec ¼ 7633e0:0856UPV
2
0.66
(14)
0.48
(15)
Types of aggregate
s/a
Brick chips
0.36
Ec ¼ 2981e
0.40 0.44 Crushed stone
0:0672UPV 2
Ec ¼ 10; 425e
0.36
Ec ¼ 7702e0:0547UPV
2
0.89
(16)
0.40
Ec ¼ 8001e0:0570UPV
2
0.89
(17)
0:0514UPV 2
0.60
(18)
0.80
(19)
0.34
(20)
0.37
(21)
0.44 Round-shaped stone
Relationship between UPV and compressive strength
Ec ¼ 9394e
0.36
Ec ¼ 8648e0:0429UPV
0.40
Ec ¼ 11567e0:0325UPV
0.44
Ec ¼ 12; 379e0:0320UPV
2 2 2
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Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Effect of types of aggregate and sand-to-aggregate volume ratio on UPV in concrete Tarek Uddin Mohammed, Md Nafiur Rahman ⇑ Department of Civil and Environmental Engineering, Islamic University of Technology (IUT), Board Bazar, Gazipur 1704, Bangladesh
h i g h l i g h t s Variation of UPV in concrete with types of aggregates and s/a. Four different types of aggregate were investigated. s/a ratios were 0.36, 0.40, and 0.44. UPV in concrete significantly influenced by the types of aggregate and s/a. With the increase of s/a, UPV in concrete is reduced.
a r t i c l e
i n f o
Article history: Received 27 April 2016 Received in revised form 6 July 2016 Accepted 25 August 2016
Keywords: Brick chips Compressive strength Modulus of elasticity Sand to aggregate volume ratio UPV
a b s t r a c t An experimental investigation was carried out to understand the variation of ultrasonic pulse velocity (UPV) in concrete with the types of coarse aggregate and sand-to-aggregate volume ratio (s/a). The types of aggregate investigated were brick chips, crushed stone, round shaped stone and black stone. Sand-toaggregate ratios were 0.36, 0.40, and 0.44 and W/C ratios were 0.45, 0.50, and 0.55. Concrete specimens were made and tested for UPV, compressive strength, and modulus of elasticity. UPV in concrete is significantly influenced by the types of aggregate and s/a ratio in addition to the compressive strength of concrete. UPV in concrete is reduced with the increase of s/a ratio. Relationships between UPV and compressive strength, and UPV and modulus of elasticity are proposed for aggregates investigated. Ó 2016 Elsevier Ltd. All rights reserved.
1. Introduction From the viewpoint of structural health evaluation of concrete structures, ultrasonic pulse velocity (UPV) in concrete has been found to be an important parameter. Many investigations were carried out to understand the variation of UPV with compressive strength of concrete [1–7]. To establish the correlations between UPV and compressive strength, different studies were carried out with the variation of types of aggregate [1,8–10], maximum size of aggregate [11–14], different grades of recycled aggregates [15,16], absorption [17], age [1,2,18,19], workability [20], W/C [2,21], and porosity of concrete [22]. It had been established that similar to compressive strength, UPV of concrete also develops with age and it is inversely proportional with volume of pores in concrete [15]. Rate of change of UPV in concrete with time can be used not only to determine the setting of concrete but also to ⇑ Corresponding author. E-mail addresses: [email protected] (T.U. Mohammed), [email protected] (M.N. Rahman). http://dx.doi.org/10.1016/j.conbuildmat.2016.08.102 0950-0618/Ó 2016 Elsevier Ltd. All rights reserved.
indicate different stages of microstructural changes at early ages of concrete [23,24]. It had been also found that UPV is affected by the microstructural variations in mortar and can be used to estimate sand content in mortar effectively [25]. UPV of concrete was also studied to detect damage inside the concrete [26–28]. Also evaluations of UPV for different types of concrete like lightweight or asphalt concrete were also conducted [29,30]. Recently, different types of statistical approach had been taken to predict compressive strength of concrete from UPV using Principle Component Analysis (PCA) and Artificial Neural Network (ANN) where compressive strength can be predicted for a variety of mix proportions and types of aggregate with a relatively smaller margin of error [8,25]. Structural health of RC structures was also evaluated by UPV [31]. Although many researchers carried out detailed investigations to understand how UPV of concrete varies with compressive strength, very limited number of literatures were found where sand-to-aggregate (s/a) volume ratio was considered as a governing parameter. As sand-to-aggregate (s/a) volume ratio has a significant influence on compressive strength of concrete,
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therefore, it is necessary to investigate how UPV of concrete varies with s/a ratios. It can be noted that s/a of existing concrete structures can be estimated based on the mix design of concrete or cut section of a structural element. For accurate estimation of compressive strength from UPV, s/a ratio is to be carefully determined. Previous studies confirm that variation of UPV in concrete made with different types of aggregate primarily accounts for two important variables, one is the acoustic impedance property and another is the quality of the aggregates [17,32]. In Bangladesh, some detailed investigations were carried out to understand the mechanical behavior of concrete made with different types of aggregates including recycled aggregates [33–35]. Studies are still necessary to correlate compressive strength with UPV for concrete made with different aggregates. Recently in Bangladesh, after the collapse of a garments factory that killed more than 3000 workers, it becomes an important task to the civil engineers to assess the safety of the existing structures. For safety assessment, evaluation of compressive strength of concrete is an important requirement. Determination of compressive strength by cutting core is not an easy method. Also, cutting cores from columns may hamper the load carrying capacity of the columns. On the other hand, UPV through concrete can be evaluated easily for different structural elements. Most of the RC structures in Bangladesh are made of brick aggregates due to lack of availability of stone aggregates. Sometimes crushed stone, round shaped stone aggregate (locally known as shingles) and black stone (extracted from quarry) are also used. Therefore, it is necessary to make a comprehensive study on the effect of different types of aggregate on UPV of concrete. As s/a ratio may change depending on mixture proportions of concrete,
Round Shaped Stone
therefore investigations on the variation of UPV with s/a are necessary. With the above-mentioned background, a detailed experimental investigation was carried out by varying types of aggregate, s/ a, and W/C. UPV in concrete made with different types of aggregate is compared and several relationships are proposed for evaluation of compressive strength, and modulus of elasticity of concrete from UPV. The results will be very useful for evaluation of structural health of existing concrete structures.
2. Experimental method 2.1. Materials Coarse aggregates investigated in this study include brick chips, crushed stone, round shaped stone, and black stone as shown in Fig. 1. Natural river sand was used as fine aggregate. The aggregates were tested for specific gravity, absorption capacity, fineness modulus, and abrasion according to ASTM specifications. The chemical compositions (determined using X-ray Fluorescence (XRF) Spectroscopy) and physical properties of coarse aggregates are summarized in Tables 1 and 2 respectively. The maximum size of coarse aggregate was 19 mm. The grading of aggregates was controlled as per the requirement of ASTM C33 as shown in Fig. 2. The specific gravity (SSD), absorption capacity, fineness modulus and unit weight of fine aggregate were 2.45, 3.30%, 2.52 and 1520 kg/m3 respectively. CEM type II/A-M (as per BDS EN 197–1:2000) was used which consists of 80–94% clinker and 6–20% of mineral admixture and gypsum.
Crushed Stone
Black Stone
Brick Chips Fig. 1. Coarse aggregates investigated in this study.
Table 1 Chemical compositions of coarse aggregates investigated. Oxides (% by weight)
CaO
SiO2
Al2O3
Fe2O3
MgO
Na2O
K2O
Others
Brick chips (BC) Crushed stone (CS) Round shaped stone (SG) Black stone (BS)
8.67 1.25 – 12.56
53.42 88.23 74.12 58.35
15.29 0.14 3.78 11.41
8.24 0.84 0.61 11.39
4.06 0.27 0.73 1.80
0.83 0.51 – 0.21
0.24 0.29 – 0.02
9.25 8.47 20.76 4.26
Table 2 Physical properties of coarse aggregates investigated. Type of coarse aggregate
Fineness modulus (FM)
% Wear
Bulk specific gravity in SSD condition
Absorption capacity (%)
Unit weight (kg/m3)
Brick chips (BC) Crushed stone (CS) Round shaped stone (SG) Black stone (BS)
Controlled as per ASTM C33
38.26 38.76 27.3 10.9
2.30 2.56 2.58 2.84
15.06 2.39 1.16 1.45
1236 1549 1671 1836
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Fig. 2. Grading of coarse aggregate (Left) and fine aggregate (Right).
2.2. Mixture proportion and specimen preparation For this study, 100 mm 200 mm cylindrical concrete specimens were made with sand to aggregate (s/a) volume ratios of 0.36, 0.40, and 0.44. s/a is defined as the ratio of absolute volume of fine aggregate to absolute volume of coarse and fine aggregate
per unit volume of concrete. Water to cement (W/C) ratios were 0.45, 0.50, and 0.55. The specimens were made for different types of coarse aggregate such as brick chips (BC), crushed stone (CS), round shaped stone (SG), and black stone (BS). The mixture proportions for all cases investigated are summarized in Table 3. As summarized in Table 3, for each type of aggregate nine different
Table 3 Mixture proportions of concrete. Type of aggregate
Notation of case
Brick chips
BC-45-36-395 BC-50-36-372 BC-55-36-351 BC-45-40-395 BC-50-40-372 BC-55-40-351 BC-45-44-395 BC-50-44-372 BC-55-44-351 CS-45-36-395 CS-50-36-372 CS-55-36-351 CS-45-40-395 CS-50-40-372 CS-55-40-351 CS-45-44-395 CS-50-44-372 CS-55-44-351 SG-45-36-395 SG-50-36-372 SG-55-36-351 SG-45-40-395 SG-50-40-372 SG-55-40-351 SG-45-44-395 SG-50-44-372 SG-55-44-351 BS-45-36-395 BS-50-36-372 BS-45-40-395 BS-50-40-372 BS-45-44-395 BS-50-44-372
Crushed stone
Round shaped stone
Black stone
W/C
0.45 0.50 0.55 0.45 0.50 0.55 0.45 0.50 0.55 0.45 0.50 0.55 0.45 0.50 0.55 0.45 0.50 0.55 0.45 0.50 0.55 0.45 0.50 0.55 0.45 0.50 0.55 0.45 0.50 0.45 0.50 0.45 0.50
s/a
0.36
0.40
0.44
0.36
0.40
0.44
0.36
0.40
0.44
0.36 0.40 0.44
Cement paste (%)
Mixture proportion, kg/m3 Cement
Water
Fine aggregate
Coarse aggregate
32
395 372 351 395 372 351 395 372 351 395 372 351 395 372 351 395 372 351 395 372 351 395 372 351 395 372 351 395 372 395 372 395 372
178 186 193 178 186 193 178 186 193 178 186 193 178 186 193 178 186 193 178 186 193 178 186 193 178 186 193 178 186 178 186 178 186
588
980
652
919
718
857
588
1091
652
1023
718
955
588
1110
652
1031
718
962
588
1211
652
1135
718
1059
Unit weight of fresh concrete (kg/m3)
28-Day compressive strength (MPa)
2141 2126 2112 2144 2129 2115 2148 2133 2119 2252 2237 2223 2248 2233 2219 2246 2231 2217 2271 2256 2242 2256 2241 2227 2253 2238 2224 2372 2357 2360 2345 2350 2335
17.3 15.9 14.9 23.1 17.3 16.7 26.7 21.5 20.3 25.5 19.6 17.9 27.2 22.5 20.9 30.7 24.7 23.7 23.2 18.2 16.8 25.5 20.5 19.2 28.4 22.4 21.2 26.4 22.7 30.4 27.5 33.2 25.6
Explanation of notations – the first two alphabets indicate type of aggregate (for brick chips-BC, crushed stone-CS, round shaped stone-SG, and black stone-BS), second two digits indicate W/C, third two digits indicate sand to total aggregate (s/a) ratio in %, and the last three digits indicate cement content in kg/m3. W/C – water-to-cement ratio; s/ a – sand to total aggregate volume ratio.
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cases were investigated. The number of cases investigated for black stone aggregate was six. The volume of cement paste content was kept constant at 32% i.e. 32% of total volume of concrete is filled with cement and water. Altogether 408 concrete specimens were made for 33 different cases. Unit weight of fresh concrete and 28-day compressive strength are also summarized in Table 3. In the mix proportions, cement and water contents were adjusted with the change of W/C to fix the volume of cement paste at 32%. Irrespective of types of coarse aggregate being investigated, the absolute volume of coarse aggregate (VCA) and fine aggregate (VFA) were kept constant for each s/a ratio. So the fine aggregate content is kept same for different types of coarse aggregate but coarse aggregate contents is changed based on the specific gravity of the type of coarse aggregate. The volume of cement paste is defined as:
Cement Paste ð%Þ ¼
100 ðV c þ V w Þ ðV c þ V w þ V CA þ V FA Þ
ð1Þ
where Vc = Absolute volume of cement, Vw = Volume of water, VCA = Absolute volume of coarse aggregate, and VFA = Absolute volume of fine aggregate per unit volume of concrete. Concrete specimens were casted in steel molds and kept under a humid environment for 24 h. The specimens were demolded after 24 h of casting and kept in underwater till the age of testing.
Prior to compressive strength test, concrete specimens were tested for ultrasonic pulse velocity (UPV) as per ASTM C597 by using Portable Ultrasonic Non-destructive Digital Indicating Tester (PUNDIT). The transducers of the pulse meter were held firmly along the length of the concrete specimen. Castrol Pyroplex Blue grease was used as couplant to ensure full contact between the transducers and the specimen. The time required by the pulse to travel from transmitting end to the receiver end of transducers was recorded for determination of UPV. For each cylindrical specimen, UPV along the axis of the specimen was measured three times and the average value was used for discussion. Nominal frequency of the ultrasonic pulse meter was 54 kHz. A photograph of measurement of UPV in concrete is shown in Fig. 3. The concrete specimens are also tested for compressive strength as per ASTM C39, and modulus of elasticity of concrete at the ages of 7, 28, 60, and 90 days. Modulus of elasticity was determined from stress-strain curve of concrete. The modulus of elasticity was determined by dividing compressive stress at strain level 0.0005. Tests for black stone aggregate were carried out at 28 days only due to limited number of specimens. 3. Results and discussions 3.1. Influence of types of aggregate on UPV The variation of UPV and compressive strength of concrete made with brick chips, crushed stone, round shaped stone, and black stone at the age of 28 days are shown in Figs. 4 and 5 respectively. The ranges of UPV and compressive strength of concrete for different aggregates are summarized in Table 4. The lowest UPV and compressive strength are found for concrete made with brick aggregate where the highest UPV and compressive strength are found for concrete made with black stone. As summarized in experimental method (Table 2), brick chips had the highest absorption capacity, lowest specific gravity and unit weight among the other coarse aggregates investigated. Coarse aggregate with high absorption capacity contains a lot of pores. These pores reduce UPV as it tries to pass through the concrete specimens. It is understood that aggregate with higher absorption capacity and less unit weight contributes to lesser UPV in concrete.
Fig. 3. Measurement of UPV through concrete.
Brick Chips
2.3. Testing of specimens
Crushed Stone
Round Shaped stone
Fig. 4. UPV of concrete made with different types of aggregate at 28 days.
Black Stone
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Fig. 5. Compressive strength of concrete made with different types of aggregate at 28 days.
Table 4 Range of UPV of concrete made with different types of aggregate. Type of aggregate
Compressive strength (MPa)
UPV through concrete (m/s)
Brick chips (BC) Crushed stone (CS) Round shaped stone (SG) Black stone (BS)
14.7–26.7 17.4–30.7 16.7–28.4 22.7–33.2
3290–3660 4273–4395 4326–4601 4610–4731
In case of black stone, the lowest wear value (Table 2) indicates that it was the strongest among the aggregate investigated in this study. Also, it had shown the highest specific gravity and unit weight among the other aggregates implying that the aggregate was relatively dense. The denser and stronger physical property of the aggregate allowed UPV to travel faster in concrete made with black stone and also gives the highest strength compared to similar cases of coarse aggregates investigated. UPV of concrete made with round shaped stone is slightly better compared to UPV of concrete made with crushed stone. This is because the round shaped stone can be judged as relatively stronger and denser
compared to crushed stone based on the results of specific gravity and wear value (Table 2). As a result, the ultrasonic pulse travels faster in concrete made with round shaped stone. But round shaped stone gives lower compressive strength, which is expected due to less interlocking of the aggregate and relatively poor quality of interfacial transition zone (ITZ) [36]. It is observed that irrespective of the types of aggregate, compressive strength and UPV of concrete are reduced with the increase of W/C. It is also noted that with the increase of s/a, compressive strength is increased but UPV is reduced. It is clear that UPV varies with types of aggregate being investigated. Thus it is difficult to establish a generalized relationship between compressive strength of concrete and UPV without considering the type of aggregate used in concrete. UPV in concrete with respect to type of aggregates can be ordered as black stone > round shaped stone > crushed stone > brick chips for similar level of strength. 3.2. Influence of age on UPV The variations of UPV and compressive strength with age are shown in Fig. 6. Irrespective of the types of aggregate, UPV is increased with time due to the development of strength of
Round Shaped Stone Crushed Stone Brick Chips
Fig. 6. Development of UPV and compressive strength with age of concrete.
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concrete for continuous hydration of cement. It is found that concrete made with crushed stone shows higher compressive strength than concrete made with round shaped stone aggregate. But UPV is found to be higher for concrete made with round shaped stone aggregate compared to crushed stone. It is because of better physical properties of round shaped aggregate, such as lower absorption capacity and relatively lower wear value (Table 2). On the other hand, relatively higher compressive strength for concrete made with stone chips can be explained due to better aggregate interlocking due to its angularity and also formation of an improved interfacial transition (ITZ) zone around the aggregate compared to smooth and round shaped aggregate [36]. The rate of increase of UPV at early age is higher for concrete made with round shaped stone and crushed stone compared to brick chips. The rate of increase of UPV with time for brick chips is lower compared to the other aggregates. Variation of compressive strength and UPV with time for black stone aggregate is not included here as the aggregate was tested at 28-day only. Based on the data of 28-day, it is understood that concrete made with black stone will give higher compressive strength of concrete compared to concrete made with other coarse aggregates due to the better physical properties of aggregate as summarized in Table 2.
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3.3. Influence of s/a on UPV The variations of compressive strength of concrete with UPV for different types of aggregates and different s/a ratios are shown in Fig. 7. Due to limited number of data for black stone, the lines are not shown for this type of aggregate. It is observed that for a given compressive strength, concrete made with round shaped stone shows the highest UPV. Concrete made with crushed stone shows comparatively lower UPV. The lowest UPV is observed for concrete made with brick chips. Similar trend of results is obtained for all s/a ratios. It is also observed that at 28-day, black stone shows similar UPV to round shaped stone. The results prove that irrespective of s/a ratio, the type of aggregate has significant influence on UPV in concrete. Same as the previous sections, ultrasonic pulse velocity of concrete with respect to type of aggregate can be ordered as black stone > round shaped stone > crushed stone > brick chips. To investigate how the pulse velocity of concrete made with same type of aggregate varies with different s/a ratios, compressive strength is plotted against UPV in concrete made with brick chips, crushed stone, and round shaped stone as shown in Fig. 8. It is observed that irrespective of type of aggregate,
Fig. 7. Compressive strength vs pulse velocity for different types of aggregate with respect to s/a ratio.
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To explain the results with further details, compressive strength and UPV in concrete made with different types of aggregate are plotted for each s/a ratio for W/C of 0.55 and cement content of 351 kg/m3 as shown in Fig. 9. It is observed that with the increase of s/a ratio, compressive strength of concrete is increased irrespective of type of aggregate but pulse velocity of concrete is reduced. The increase in s/a ratio (from 0.36 to 0.44) results in better compaction of concrete that gives more compressive strength of concrete. Again, with the increase of s/a ratio, coarse aggregate content in concrete is reduced, therefore UPV is reduced. It is clearly understood that in order to predict compressive strength of concrete from UPV with reasonable accuracy, s/a ratio should be considered as a governing parameter in addition to the types of aggregate. 3.4. Relationships between compressive strength and UPV with the variation of s/a Based on Fig. 8, relationships were developed between 0 compressive strength (f c) and UPV in concrete for different aggregates with the variation of s/a. The results are summarized in Table 5. The exponential relationships of Table 5 can be expressed in the following generalized form: 0
f c ¼ A eBUPV
ð11Þ
where ‘‘A” and ‘‘B” are coefficients of the exponential equation. ‘A’ indicates the position of exponential lines from the axis of compressive strength. The more is the values of ‘A’, the more is the shifting of graphs from the axis of compressive strength. From the exponential relationships, it is found that the value of ‘A’ is different for different types of aggregate (highest for crushed stone then round shaped stone then brick aggregate). Also, the value of ‘A’ is decreased with the increase of s/a. Coefficient ‘B’ indicates the rate of change of compressive strength with UPV. Interestingly, it is noted that for a particular type of aggregate, the value of ‘B’ is almost constant irrespective of s/a. Based on this observation, compressive strength and UPV in concrete can be represented by the following relationships for different aggregates investigated: 0
f c ¼ K A eBUPV
ð12Þ
where ‘K’ is a factor related to s/a ratio. The values of A, B, and K are summarized in Table 6. 3.5. Relationships between modulus of elasticity and UPV
Fig. 8. Compressive strength vs pulse velocity of concrete.
pulse velocity of concrete varies with s/a ratio. The lines move rightward in parallel with the decrease of s/a. It is clearly observed that for the same strength of concrete, UPV is reduced with the increase of s/a. It is also understood that an exponential relationship between compressive strength and UPV can be formed for each type of aggregate with an inclusion of a factor related to s/a. From Fig. 7, it is also found that the compressive strength versus UPV lines are not parallel for different aggregates. Therefore, a general exponential equation cannot be formed between UPV and compressive strength for all aggregates. The relationships between UPV and compressive strength are explained in the next section.
An attempt was also made to correlate compressive strength of concrete with squared value of UPV. Similar type of relationships are also proposed by other researchers [14]. The results are shown in Fig. 10. It is found that for each type of aggregate, the lines move rightward in parallel with the decrease of s/a. Exponential relationships are developed between modulus of elasticity and UPV2 for different aggregates and different s/a. The results are summarized in Table 7. Even though the data are dispersed, but an attempt has been made to derive a simple relationship that can be used for prediction of compressive strength and Young’s Modulus from UPV. Similar level of dispersions of data can also be found in other literature [4,5,11,37]. The exponential relationships between modulus of elasticity (Ec ) and UPV can be expressed by the following equation:
Ec ¼ A eBUPV
2
ð22Þ
839
T.U. Mohammed, M.N. Rahman / Construction and Building Materials 125 (2016) 832–841
Fig. 9. Effect of s/a ratio on strength and UPV (W/C – 0.55 and Cement content – 351 kg/m3). Table 5 Relationships between compressive strength and UPV of concrete for different aggregates with the variation of s/a. Types of aggregate
s/a
R2 value
Equation number
0
0.82 0.73 0.51
(2) (3) (4)
0
0.74 0.75 0.81
(5) (6) (7)
0
0.79 0.93 0.91
(8) (9) (10)
Relationship between UPV and compressive strength
Brick chips
0.36 0.40 0.44
fc ¼ 0:8944e0:00080UPV 0 fc ¼ 0:3599e0:00115UPV 0 fc ¼ 0:1662e0:00140UPV
Crushed stone
0.36 0.40 0.44
fc ¼ 1:2277e0:000660UPV 0 fc ¼ 1:2003e0:000680UPV 0 fc ¼ 1:1502e0:00070UPV
Round-shaped stone
0.36 0.40 0.44
fc ¼ 0:5836e0:00080UPV 0 fc ¼ 0:5201e0:00085UPV 0 fc ¼ 0:4719e0:00090UPV
Table 6 0 Values of A, B, and K for exponential relationships between f c and UPV. Types of Aggregate
s/a
Values of A, B and K A
B
K
Brick chips
0.44 0.40 0.36
0.1662
0.0014
1 0.922 0.685
Stone chips
0.44 0.40 0.36
1.1502
0.0007
1 0.969 0927
Round shaped stone
0.44 0.40 0.36
0.471
0.0009
1 0.922 0.871
840
T.U. Mohammed, M.N. Rahman / Construction and Building Materials 125 (2016) 832–841 Table 8 Values of A, B, and K for relationships between Ec and UPV2. Types of aggregate
s/a
Values of A, B and K A
B
K
Brick chips
0.44 0.40 0.36
10425
0.0672
1 0.919 0.765
Stone chips
0.44 0.40 0.36
9394
0.0514
1 0.913 0.854
Round shaped stone
0.44 0.40 0.36
12379
0.032
1 0.941 0.799
value of ‘A’ is increased with the increase of s/a. It is also found that the value of ‘B’ is almost constant for a particular type of aggregate irrespective of s/a. The relationship can be further generalized in the following form:
Ec ¼ K A eBUPV
2
ð23Þ
where ‘K’ is a factor related to s/a. The values of A, B, and K are summarized in Table 8. 4. Conclusions From the scope of this investigation, the following conclusions are drawn: UPV in concrete is strongly influenced by the types of aggregate and s/a ratio. UPV of concrete can be ordered as black stone > round shaped stone > crushed stone > brick chips for the same strength of concrete. With the increase of s/a ratio, UPV of concrete is reduced. Exponential relationships are proposed between compressive strength of concrete and UPV for different aggregates with incorporation of a factor related to s/a ratio. Exponential relationships are proposed between modulus of elasticity of concrete and squared values of UPV for different aggregates with incorporation of a factor related to s/a ratio.
Acknowledgments Fig. 10. Relationship between modulus of elasticity and UPV.
From the exponential relationships, it is found that the value of ‘A’ is different for different types of aggregate (highest for round shaped stone then crushed stone then brick aggregate). Also, the
The authors acknowledge the financial support and facilities provided by Islamic University of Technology (IUT) for research works in the field of concrete technology at the Department of Civil and Environmental Engineering (CEE). The authors also wish to express their gratitude to Seven Circle Bangladesh Ltd. for providing materials for this study.
Table 7 Relationships between Young’s modulus and UPV of concrete for different aggregates with the variation of s/a. R2 value
Equation number
0:1459UPV
2
0.66
(13)
Ec ¼ 7633e0:0856UPV
2
0.66
(14)
0.48
(15)
Types of aggregate
s/a
Brick chips
0.36
Ec ¼ 2981e
0.40 0.44 Crushed stone
0:0672UPV 2
Ec ¼ 10; 425e
0.36
Ec ¼ 7702e0:0547UPV
2
0.89
(16)
0.40
Ec ¼ 8001e0:0570UPV
2
0.89
(17)
0:0514UPV 2
0.60
(18)
0.80
(19)
0.34
(20)
0.37
(21)
0.44 Round-shaped stone
Relationship between UPV and compressive strength
Ec ¼ 9394e
0.36
Ec ¼ 8648e0:0429UPV
0.40
Ec ¼ 11567e0:0325UPV
0.44
Ec ¼ 12; 379e0:0320UPV
2 2 2
T.U. Mohammed, M.N. Rahman / Construction and Building Materials 125 (2016) 832–841
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