The effects of grinding on the properties of Portland-limestone cement

Construction and Building Materials 48 (2013) 1145–1155

Contents lists available at ScienceDirect

Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat

The effects of grinding on the properties of Portland-limestone cement A. Marzouki a,d, A. Lecomte b,⇑, A. Beddey c, C. Diliberto b, M. Ben Ouezdou a,e a

Civil Engineering Laboratory, National Engineering School of Tunis, University of Tunis El Manar, BP 37, 1002 Tunis Belvédère, Tunisia Institut Jean Lamour, UMR 7198, CP2S, Materials for Civil Engineering, University of Lorraine, IUTNB, CS 90137, F54600 Villers-lès-Nancy, France c Centre d’Etudes Techniques et d’Essais de Construction (C.E.T.E.C), Av, 15 Octobre 1009, Ouardia, Tunisia d Higher Institute for Technological Studies of Radès, ISET Radès, BP 172, 2098 Radès Medina, Tunisia e Civil Engineering Department, American University of Shrajah, POB 26666, Sharjah, United Arab Emirates b

h i g h l i g h t s  It is shown that the grinding quality greatly controls the properties of Portland-limestone cement.  It is especially the fineness of Portland clinker that is important because the limestone (more soft) is always finer.  Crushed limestone (fillers) behaves like crushed Portland clinker for the powder packing density and the pastes consistency.  It improves the performance at young age (by formation of hemicarboaluminate), especially when the cement is well crushed.  But a very fine grinding does not compensate for completely a significant presence of limestone.

a r t i c l e

i n f o

Article history: Received 26 January 2013 Received in revised form 11 July 2013 Accepted 21 July 2013 Available online 26 August 2013 Keywords: Portland-limestone-cement Grinding Strength Porosity Stability Sorptivity

a b s t r a c t This paper presents a study of seven Tunisian cements with varying limestone filler content, manufactured on an industrial scale. The purpose of the study is to promote Portland-limestone cement in countries where these cements are not usually used. Materials characterization showed that the grinding quality of the seven cements was very different. This parameter was defined by the ratio of specific surface (Blaine) and residue at 40 lm. Generally limestone fillers behave in a similar way to crushed clinker although they do accelerate the setting because they are finer. Monocarboaluminate appeared from a young age when filler content was high. At a young age (2 days), mechanical strengths are equivalent, at least if grinding quality is satisfactory. At a medium age (28 days), grinding quality influences performance. At a later age (1 year), only those cements with high limestone content underperform. Limestone fillers increase sorptivity and modify porosity but have little influence on dimensional stability. Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction Cement blended with limestone is known around the world. Its use has interesting economic and environmental advantages as it allows a reduction in energy consumption [1] and greenhouse gas emissions. It should be noted that a ton of clinker releases about one ton of CO2 following limestone calcinations (50–60%), combustion-related emissions (30–35%) and emissions from the transport of elaborated and raw materials [2,3]. In Tunisia, the cement industry alone accounts for nearly 40% of the energy consumed by the industrial sector [4], and about 80% of the building materials sector. In 2009, the production of one ton of clinker required more than 1100 therms which figure represents over half of its cost. In the same year, CO2 emissions reached 2600 kMTCO2 (kilo metric tons of CO2 equivalent) [4], i.e., half of ⇑ Corresponding author. Tel.: +33 (0) 3 83 68 25 75. E-mail address: [email protected] (A. Lecomte). 0950-0618/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2013.07.053

the total emissions from the country’s manufacturing sector. In this context, in order to limit environmental impact, the Tunisian cement manufacturers now offer two types of Portland-limestone cement in conformity with Tunisian standard NT 47.01 [5] (equivalent to European standard EN 197-1): CEMII/A-L containing 18–20% of limestone fillers and CEMII/B-L containing 30–35% of limestone fillers. These contents are close to the maximum limit of each category. However, in practice these cements are rarely used because public project specifications [6] prohibit their use in structural concretes. Moreover, cements CEMII/B-L are only manufactured for export and are therefore not available for the domestic market. In the neighboring country, Algeria, the national standard limits the maximum content of limestone fillers in Portland cements to 5% [7]. But the availability of other mineral constituents, such as blast furnace slag, fly ash and natural pozzolans allows the development of a variety of Portland composite cement (PCC etc.). In Europe, the production of limestone cement varies from one country to another depending on the uses and

1146

A. Marzouki et al. / Construction and Building Materials 48 (2013) 1145–1155

availability of other mineral constituents. In France, the standardized cements NF EN 197-1 incorporating limestone fillers have been used for over 25 years in many applications and various exposure conditions [2]. In 2004, they represented 32% of cements used [8]. From a scientific viewpoint, much research on cements with limestone additions have been carried out. The majority of this research has shown that limestone fillers influence the reactivity and the hydration kinetics of clinker. Mechanical strength is little affected, at least for moderate rates of limestone fillers. It is, however, influenced by clinker quality, limestone quality and fineness of addition [9–12]. Other research has reported an increase in shrinkage [13,14] especially in hot environments [15]. Some researches [13] recommend avoiding the use of cements containing limestone fillers in construction, or even any cement containing mineral additives. The results of these studies, which are sometimes contradictory, show that the addition of limestone in cement has variable effects on the properties of the mixture, particularly depending on the nature of the constituents and exposure conditions. It should be remembered that each Portland clinker is unique since it is derived from local raw materials, and that each limestone also has its own specificities. It is therefore necessary to study the mixture of these two constituents case by case in order to verify their affinity and guarantee the quality of the cement produced. It is one of the objectives of this study, i.e. to show at the designers and users, especially those from Tunisia, that it is possible to produce and use limestone cements which meet the standard technological requirements. This includes the requirements of public works. This cement has less economic and environmental impact compared to those relating to the pure Portland cement currently in use. Currently, seven cement plants found throughout Tunisia produce a variable quality of clinkers and cements. For this study, one of them manufactured seven composite cements with increasing amounts of the same limestone with the same clinker. These cements were used to prepare pastes, mortars and concrete that underwent the usual tests. Only those results obtained on pastes and mortars are presented in this paper. They were related, not only to the amount of limestone fillers present in cements, but also to the grinding quality which varied significantly from one product to another. First we present the materials and then we detail the physicochemical, mechanical and dimensional stability properties obtained, mostly in relation to grinding quality.

2. Materials The seven cements in this study were manufactured by the intergrinding of clinker, limestone and natural gypsum on an industrial scale. The properties of these three raw materials are presented below.

2.1. Clinker, limestone, gypsum A chemical analysis (XRF, LOI, free lime, etc.) of these materials is given in Table 1. The values obtained are regular but reveal that limestone and gypsum contain a significant silica content of about 4%. The clinker mineralogy was calculated with Bogue’s equations, according to ASTM standard C150. The corresponding values are given in Table 2, with composition intervals suggested by Taylor [16] and the various modules associated with calculation. We verified the correct compliance of clinker with the Tunisian specifications, whose main requirements with their normative references are noted in Table 3. The low content of free lime which is observed confirms the balance of raw mix and the quality of the burning and quenching of clinker. We also noted the low alkali content. The limestone mineralogy was determined from oxide content and loss of ignition and is shown in Table 2. Its calcium carbonate content (CaCO3) is much higher for use as a principal component of composite cements than the minimal normative

Table 1 Chemical analyses of clinker, limestone and natural gypsum (XRF, LOI, and free lime). Oxides

Clinker

Limestone

Gypsum

CaO SiO2 Al2O3 Fe2O3 SO3 K2O Na2O MgO Cl (ppm) CaO(free) Na2Oeq H2O LOI500 °C LOI950 °C

66.22 22.26 5.03 3.09 0.82 0.48 0.12 1.34 166.40 1.39 0.44 – – –

51.77 3.67 0.53 0.35 0.71 0.06 – 0.26 340 – – 1.82 0.86 41.60

32.14 4.30 0.44 0.25 40.47 0.07 – 0.60 398 – – 7.58 14.19 19.61

limit of 75% [5]. This limestone also contains a significant fraction of silica in the form of quartz. Finally, the total organic carbon content was determined by the cement factory and is classified in category L of standard [5]. The natural gypsum mineralogy deduced from chemical analysis shows that this material contains calcium carbonate (12%), silica/quartz (5%) and calcium sulfate probably not completely dehydrated, taking into account the chemical assessment. Approximately 69% of anhydrous calcium sulfate (CaSO4) was obtained. 2.2. Cements In order to manufacture each type of cement, a mass of clinker (K) was substituted by limestone (L) at the time of grinding, in proportions shown in Table 4. This table also identifies the cements used in this study. The percentage (%L) represents the mass of limestone in cement C (C = K + L), that is:

%L ¼

L K þL

ð1Þ

It is equal to 0% (reference cement), 5%, 12%, 20%, 25%, 30% and 35%, respectively. There are seven cements corresponding to standard categories [5] CEM I, CEM II/A-L and CEM II/B-L (see Table 4). Chemical analysis of the cements (Table 5) was determined by XRF, with supplementary measurements of insoluble residue and free lime content. TGA–DTA analyses were also carried out on each type of cement to confirm their limestone content (unit SETARAM TG/DTA 92–16.18, 10 °C/min until 950 °C, under argon atmosphere). The contents of calcium oxide reagent (CaOR) and silicon dioxide reagent (SiO2R) were calculated from the results of these analyses as follows:

CaOR ¼ CaOt  CaOa  CaOb and SiO2R ¼ SiO2t  IR

ð2Þ

where CaOt is the total proportion of CaO given by XRF analysis, CaOa is the proportion of CaO calculated from CaCO3 (TGA), CaOb is the proportion of CaO in CaSO4, after deducting the quantity of SO3 fixed by alkalines, SiO2t is the total proportion given by XRF analysis, IR is the insoluble residue. It should be remembered that standard NT 47.01 impose a percentage in mass of above 50% of these two elements, which is verified for all cements, including that containing 35% of limestone (Table 6). As limestone addition increases, the mass content of the other constituents decreases, leading to a modification of most of the physical characteristics of these cements. For example, the loss of ignition increases with limestone content, going from 1% for reference cement C0 to about 16% for cement C35L (for C0, the value derives from calcium sulfate which contains 12% calcite, see Table 2). Similarly, the insoluble residue content increases due to the quartz content of limestone and gypsum (Table 2). Conversely, the percentage of calcium sulfate expressed by SO3 content remains almost constant, which clearly indicates that this addition does not vary from one cement to another. For reference cement C0, the corresponding content of CaSO4 is about 3.9%. For the other cements, this content increases significantly, up to a value of 5.9% for cement C35L. However, these values remain lower than the limit of 6% recommended by standard [5]. The role of this element is to control the reactivity of C3A. Therefore, it would have been preferable if its proportioning had been associated with clinker content in the cement. It should be noted that the amount of calcium sulfate for each type of cement is normally optimized by the cementmanufacturer, depending on the mineralogy of its clinker and the variety of calcium sulfate used. Mineralogical analysis of the cements was carried out by X-ray diffraction (XRD, Philips with Cu Ka1 and Cu Ka2 radiation). Mineral phases were identified using the software DiffracEva-plusÒ. The XRD patterns (not communicated) indicate that in addition to the major clinker phases (C3S, C2S, C3A and C4AF), calcite is detected in all cements including the reference (calcium carbonate contained in gypsum). Quartz is detected in all cements containing limestone since the latter contains

1147

A. Marzouki et al. / Construction and Building Materials 48 (2013) 1145–1155 Table 2 Mineralogical composition of clinker, limestone and natural gypsum. Clinker

Limestone

Major phases

Content (%)

Intervals [16]

Modules

C3S C2S C3A C4AF

62.1 17.3 8.1 9.4

60–65 10–20 8–12 8–10

LSF SR AR HM

94.87 2.74 1.63 2.18

Table 3 Compliance verification of clinker according to specifications [5]. Parameters

Clinker

Limits

Reference

C3S + C2S (%) CaO/SiO2 MgO (%) Na2Oeq (%) CaOfree(%)

79.4 2.97 1.34 0.44 1.39

>66.6 >2 <5 <0.6 <2

[5] [5] [5] ASTM 150 [18]

Table 4 Limestone filler content and cement designation in the study. Limestone mass percentage (%l) 0 5 12 20 25 30 35

Factory designation

Study designation

CEM I 32.5 N (reference) CEM I 32.5 N CEM II/A-L 32.5 N CEM II/A-L 32.5 N CEM II/B-L 32.5 N CEM II/B-L 32.5 N CEMII/B-L 32.5 N

C0 C5L C12L C20L C25L C30L C35L

a

Major phases

Content (%)

Major phases

Content (%)

CaCO3 Quartz Others

92.6 3.6 3.8

CaSO4 CaCO3 Quartz

68.8 12.3 5

C5L contain both varieties, gypsum representing the majority. It is likely that these nuances are a result of the grinding (partial dehydration of di-hydrate), or a variation in the sulfate source. Three measurements were performed in order to evaluate the fineness of the cements, the specific surface Blaine (SSB) according to EN 196-6 (Table 8), laser granularity (Fig. 1) and the residue R40C at 40 lm using an Alpine air jet sieve shaker (Table 7). The loss of ignition of residue R40C was also measured to evaluate limestone content of this fraction (Table 7). It was found that the Blaine fineness of cements C0 and C5L was particularly low only 260 m2/kg. This value reflects a rather poor grinding. With limestone addition, the specific surface gradually increases (Table 8) since this mineral is softer than clinker. It reaches 480 m2/kg for cement C35L. But, as demonstrated by Tsivilis et al. [10] on a mixture of 80% clinker–20% limestone with intergrinding for 50 min in a laboratory mill, the limestone is undoubtedly concentrated in the finer fraction (<8 lm) while clinker is coarser. Our own measurements of residue at 40 lm confirm this hypothesis: the more the limestone content increases the more the residue decreases. These residues, in fact, contain much less limestone than the proportion added in the initial mixture, as shown in the CaCO3 content of cements deduced from loss on ignition of these residues (CaCO3). This measure allows the actual content of residue (%L) to be estimated at 40 lm of limestone (R40L) and clinker (R40K) according to the following equation:

%L ¼

Table 5 Chemical analyses of cements. (%)

C0

C5L

C12L

C20L

C25L

C30L

C35L

CaO SiO2 Al2O3 Fe2O3 MgO SO3 Na2O P2O5 K2O TiO2 MnO SrO CaO(free) LOI950 °C IR CaCO3a

65.22 22.30 4.92 2.95 1.36 2.26 0.14 0.07 0.33 0.26 0.04 0.05 1.00 1.02 0.66 0.79

63.70 21.25 4.89 2.76 1.36 2.73 0.22 0.07 0.40 0.25 0.04 0.04 0.60 2.87 0.75 4.67

63.48 20.04 4.36 2.54 1.24 2.34 0.11 0.07 0.35 0.23 0.04 0.05 0.96 5.70 0.58 10.59

60.90 17.74 4.01 2.28 1.16 2.64 0.09 0.06 0.26 0.21 0.04 0.04 0.70 9.65 1.49 19.56

61.45 17.00 3.73 2.18 1.06 2.54 0.11 0.06 0.31 0.19 0.03 0.04 1.08 11.20 1.28 23.20

59.42 15.81 3.48 1.98 1.12 2.37 0.10 0.06 0.25 0.18 0.03 0.04 0.70 14.34 1.93 30.74

59.96 14.85 3.34 1.87 0.96 2.21 0.09 0.05 0.20 0.17 0.03 0.03 0.60 15.83 1.56 33.37

Gypsum

CaCO3 ; 0:926

R40 L ¼

%L:R40 C ; 100

R40 K ¼

ð100  %LÞR40 C 100

ð3Þ

where 0.926 is the CaCO3 content of the limestone, R40C is the percentage of residue at 40 lm in the cement The results are given in Table 7 and Fig. 2. We notice that these residues virtually contain no limestone and that the clinker amount which they contain varies substantially from one cement to another. The grinding quality of these cements is not uniform but rather random. The granular curves confirm these measurements (Fig. 1), highlighting that cement granularity is rather different and divided into several distinct families. Based on these analyses, a ‘‘grinding quality’’ was defined for each cement, based on the two available measures; the specific surface Blaine and the clinker residue at 40 lm R40K. The ratio obtained is then an objective marker of performed grinding (Table 7). The higher this ratio, the better the grinding of cement. Thus, cement C30L is the finest, followed by cements C35L and C25L which are of inferior quality. Cements C20L, C12Land C0 follow and Cement C5L is the coarsest. Since the reactivity of cement greatly depends on the fineness of its clinker, we can predict that these products will not behave in the same way whatever their limestone filler content. The absolute density of the cement without limestone (clinker) Dab,K and that of limestone filler Dab,L were measured by two methods: pycnometry and Le Chatelier flask [17]. Toluene was used as a liquid in this density determination. The respective values are Dab,K = 3040 kg/m3 for clinker (Table 8) and Dab,L = 2702 kg/m3 for limestone. The absolute density (Dab) of the six other cements (containing %l) was deduced from the above properties according to the equation:

Dab ¼ Dab;L  %L þ Dab;K  ð1  %LÞ

ð4Þ

Calculation according to TGA–DTA analysis.

Table 6 Contents of reagent calcium oxide (CaOR) and reactive silicon dioxide (SiO2R). Cement

C0

C5L

C12L

C20L

C25L

C30L

C35L

CaOR (%) SiO2R (%) Total (%)

62.67 21.64 84.31

58.56 20.50 79.06

54.88 19.46 74.34

46.98 16.25 63.24

45.66 15.72 61.39

39.71 13.88 53.59

38.43 13.29 51.71

about 3.6% SiO2. Calcium sulfate exists as two types: gypsum in cements C20L, C25L, C30L and C35L and bassanite (1/2 hydrate) in cement C0 and C12L. Cements

Bulk density (Dbulk) was determined by weighing the contents of three identical containers (Ø 2 cm, height 4 cm) after medium and uniform vibration for all measurements. The corresponding values are shown in Table 8. As the density of limestone is lower compared to clinker, the Dab of the cements steadily decreases with the amount of limestone addition. The Dbulk also decreases, but with rather important fluctuations which are explained by the differences in product fineness, due to differences in packing density. The packing density of powder /d is calculated according to Eq. (5) (Table 8).

/d ¼

Dbulk Dab

ð5Þ

As a summary, the characterization of the seven cements shows that they do not have the expected regularity, particularly with regards to sulfate content and grinding fineness. Thus, the content of limestone fillers does not represent the only variable in this study.

1148

A. Marzouki et al. / Construction and Building Materials 48 (2013) 1145–1155

Table 7 Grinding quality of cements.

a

Cement

R40C (%)

CaCO3a %

%l (%)

R40L (%)

R40K (%)

Grinding quality SSB/R40K

C0 C5L C12L C20L C25L C30L C35L

20.4 32.8 17.2 17.7 7.5 6.1 7.4

0.4 2.7 4.6 9.5 8.2 13.8 16.0

0.4 2.9 4.9 10.2 8.8 14.9 17.3

0.1 0.9 0.8 1.8 0.7 0.9 1.3

20.3 31.9 16.4 15.9 6.8 5.2 6.1

13 8 18 21 64 91 79

CaCO3 content calculated from LOI of residue at 40 lm.

Table 8 Physical parameters measured on cements, normal pastes and constant workability mortars. Ref.

Cement

C0 C5L C12L C20L C25L C30L C35L

Pastes (normal consistency)

Dab (kg/m3)

Dbulk (kg/m3)

/d

SSB (m2/kg)

W/C

/w

3040 3023 2999 2972 2956 2939 2922

1183 1282 1101 1188 977 993 942

0.389 0.424 0.367 0.400 0.331 0.338 0.322

262 264 298 341 435 474 484

0.267 0.238 0.264 0.274 0.283 0.304 0.292

0.554 0.583 0.560 0.553 0.546 0.529 0.541

Mortars

Setting (min) Initial

Final

170 180 145 165 140 145 135

270 270 240 250 190 210 210

Expansion (mm)

W/C

1.75 2.25 1.25 0.50 1.50 0.75 1.25

0.5 0.489 0.498 0.502 0.501 0.509 0.503

3. Results and discussion 100

3.1. Pastes

C25L

Volume passing (%)

80

C5L 60 C0 C5L C12L C20L C25L C30L C35L

40

20

0 0

1

10

100

1000

Particle size (µm)

Pastes of normal consistency (Vicat consistency plunger) were produced with the various cements. The corresponding W/C ratio is given in Table 8. It is noted that it slightly increases with the filler amount, with the exception of C5L and C30L – the coarsest and finest of the batch – which require respectively less or more water than the others. However, this water requirement is not directly related to the filler amount because if we compare, for example (Fig. 3) the ‘‘grinding quality’’ of different cements and the packing density of dry powder /d, or even of the packing density of normal paste /w, we obtain good fits (semi-logarithmic scales) indicating that the finer the cement, the less it is compacted, and vice versa. Thus, water demand increases or decreases correlatively. The packing density of normal paste /w is calculated from the W/C ratio as follows:

Fig. 1. Particle size distribution for all cements obtained by lazer granulometry.

/w ¼

% of L in C

35

% of L in R40 R40 C (%)

30

R40 K (%) R40 L (%)

25 20 15 10 5 0 0

5

10

15

20

25

Fig. 2. Study of residue at 40 lm.

30

35

1000 1000 þ Dab WC

ð6Þ

That means that, the type of limestone or clinker filler does not in fact impact water demand. It is rather the granularity and the fineness, i.e. the grinding quality, that plays a role here. Thus, the limestone fillers behave in a similar way than clinker as far as the consistency of pastes is concerned. These results agree with observations made by Vuk et al. [11] and Ellerbrock et al. [19]. The initial setting time, final setting time and autoclave expansion (Le Chatelier needles) measured on standard consistency pastes are given in Table 8. The Tunisian standard [5] requirements are verified for all cements. It is noted that the higher the substitution of limestone fillers, the shorter the initial and the final setting times. For example, the initial setting time is reduced to 35 min between C0 and C35L. As described in the literature [20–23], we can assume that the fillers form nucleation sites favorable to the acceleration of hydration reactions and the growth of hydrates. The monitoring of hydration by XRD analysis was performed on three normal pastes made with cements C5L, C12L and C30L, i.e., with low, medium and high limestone filler content. The XRD

1149

A. Marzouki et al. / Construction and Building Materials 48 (2013) 1145–1155

These mortars were used to cast three prismatic specimens (4  4  16 cm) for measuring different properties. Different mortars were made on the same day and under the same conditions for the same time period. For the mechanical tests, the specimens were cured after demolding in water at approximately 20 °C (curing room without temperature control). Fig. 4 shows the evolution of the densities of mortar when the content of limestone fillers in cement increases:

Packing density ( φ d or φ w )

0,6

Paste (φ w )

0,5

C5L C20L 0,4

Powder (φ d)

C0 C12L

0,3

1

10

C30L C25L C35L 100

Grinding quality Fig. 3. Comparison of ‘‘grinding quality’’ and packing density of cement powder or normal consistency paste.

patterns at 2, 7 and 28 days (not presented) all show the presence of calcite and quartz coming from limestone. Anhydrous calcium silicates (C3S and C2S) are still present at 28 days but the relative intensity of their peaks decreases between 2 and 28 days. Gypsum and C3A are not detected even at 2 days. C4AF decreases over time and with the increase of filler rate (probably because of the decrease in clinker share). Ettringite and Portlandite are present in all pastes but, over time, the peaks of Portlandite decrease. Monosulfoaluminate is not detected. Calcium hemicarboaluminate appears in the paste within 2 days with C30L, and calcium monocarboaluminate appears in the paste with C12L and C30L at 28 days. Both these hydration products are new compared to those usually present in Portland cement. Here, we find phenomena that have already been described in the literature: – The rapid appearance of hydrated calcium monocarboaluminate (barrier developed on the surface of C3A grains), the early formation of ettringite and its conversion to monosulfoaluminate which is delayed or stopped [24] (monocarboaluminate replaces the monosulfoaluminate formation by substitution of sulfate ions with carbonate ions [23,25]). – The acceleration of C3S hydration (with the incorporation of a significant amount of CaCO3 into the structure of C–S–H gel [26]). We should note that a hydrated calcium silicocarbonate can also be formed in the presence of a large amount of limestone fillers, as described by Husson et al. [27].

– The theoretical density (Dth), calculated for the specific density of the components and their proportions, logically decreases in mortar with constant W/C ratio, since the density of cement decreases [30,31]. With constant workability, this change is not steady because of the cements’ fineness. Cements C5L (coarse) and C30L (fine), for example, (Table 7), which are compacted to varying degrees (Table 8), give mortars which require, respectively, less and more water demand (to keep the same workability), and therefore, to higher and lower densities than expected. – The apparent density (Dap) of fresh mortars with constant W/C ratio, deduced from the weighing of 4  4  16 molds, also shows a decrease, but with fluctuations which can be attributed only to the amount of trapped air (since the other constituents have not changed) and/or the grinding quality. This air calculated according to Eq. (7) is presented in Fig. 5. Its variation correlates quite well with the grinding quality of cement (Table 7) which apparently favors the departure of the air from specimens. The trapped air content of mortars with constant W/C ratio and mortars with constant workability were measured by air meter (am) after 15 s of vibration (vibrating table 50 Hz). The results are given in Fig. 5. The measured air content is usually higher than the air content calculated (ac) from the densities. This is probably due to the different geometries of the molds and the method of tightening applied. It should be remembered that calculated air (ac) is given by the equation:

  Dap ac ð%Þ ¼ 100 1  Dth

where Dth is the theoretical density of the mixture concluded from the specific density of the constituents and their respective proportions. In accordance with [32], it appears that the amount of limestone fillers favors the trapping of air especially if the consistency

Finally, from mechanical point of view, according to [28], calcium sulfoaluminate, calcium monocarboaluminate and calcium hemicarboaluminate behave similarly.

Mortars were produced according to the EN 196-1 standard. The control mortar is produced with reference cement C0 (with W/C = 0.5). Mortars with other cements were made either with constant W/C ratio (0.5) or with constant consistency (with variable W/C), adjusting the quantity of mixing water to keep the flow time of the control mortar (t0 ± 0.5 s), using a B-type LCPC workability meter [29]. The W/C ratio is shown in Table 8. It was observed that these parameters vary little with the rate of the fillers in the cement, including that of the highest rate. As for pastes, limestone fillers added to the cement do not influence the rheology of mortars; they behave like the ground clinker and only the quality of grinding comes into play.

theorical, w/c=0.5

2350

theorical, same workability

Density of mortar (Kg/m 3)

3.2. Fresh mortars

ð7Þ

real, fresh mortars (w/c=0,5)

2250

2150 0

5

10

15

20

25

Limestone content (%) Fig. 4. Density of mortars.

30

35

1150

A. Marzouki et al. / Construction and Building Materials 48 (2013) 1145–1155

of the mortar is not kept constant by modulating the water. Once again, cement fineness seems to play an important role. The heat measured on the different mortars for 5 days with a Langavant-type semi-adiabatic calorimeter is given in Fig. 6 for four time periods (12 h, 1, 3 and 5 days). It always remains less than 300 J/g, which is corresponding to the standard limit of NT 47.01 [5]. It is noted that the limestone fillers significantly reduce the release of heat up to 50 J/g after 3 and 5 days for 35% of clinker substitution. At early hydration (12 h and 1 day), this reduction is not in fact observed since the heat released remains essentially constant. Here, it is the grinding fineness of clinker which exerts its influence (see Table 7), since it increases its reactivity and its exothermy at an early age. The early formation of the hemicarboaluminate in cements rich in fillers (rather than ettringite), noted by XRD analysis (see Section 3.1), may also partially explain the variations in heat of release which are observed. The fluctuations at early age can be explained by the opposite action of the amount of limestone fillers present (which reduces heat) and the grinding quality (which increases heat).

The relative differences (%) in the ratios of theoretical strength to experimental strength were compared to the grinding quality (semi-logarithmic scale). At early ages (Fig. 9a), it can be noted that limestone fillers have an important effect on the strength and correlate quite well with grinding quality (accelerating effect). Filler amount is therefore not the only determining factor. Low filler content (i.e., high clinker

3.3. Mechanical strength

Rth ¼ K C :C 20 ¼ K C



c cþwþa

2 ; with K C ¼

Rexp

ð8Þ

C 20

Fig. 6. Heat of release as a function of limestone fillers content in cement measured on mortars at different terms.

9

6

3

0

where C0 is the compactness of the binding phase, c, w and a are the respective volumes of cement, water and air in mortar, deduced from design parameters, Rexp is the experimental strength measured at each age on the mortar made with cement C0 (without limestone fillers).

0

5

10

15

20

25

Compressive strength (MPa)

2 w/c=0.5 (experimental values) same workability (experimental values) theoretical value (w/c=0,5) 0 0

5

10

15

20

25

Limestone content (%) Fig. 5. Entrained air of fresh mortars.

30

35

35

Fig. 7. Tensile strength of mortars (W/C = 0.5).

360 days 90 days 28 days 7 days 2 days

60

4

30

Limestone content (%)

6

Mortar content air (%)

360 days 90 days 28 days 7 days 2 days

12

Tensile strength (MPa)

The mortars’ strength was measured at 2, 7, 28, 90 and 360 days, respectively. We find the same tendencies for tensile (Fig. 7) and compressive (Fig. 8) strengths of mortars with W/C = 0.5 and mortars with constant workability (Table 9). At early age (2 and 7 days), the strength remained generally stable with the filler amount, mainly due to the accelerating effect of these products. At longer time periods, the strength decreases when the filler content becomes high. In terms of absolute values, the performance of cements containing between 0% and 25% of limestone fillers remains more or less stable (Fig. 8). Only cements rich in fillers perform less well but still give respectable results. To appreciate the contribution of limestone fillers to compressive strength, the mortars’ strength was calculated assuming that the fillers play no role (only clinker). The Caquot formula was used to calculate the theoretical strength Rth (mortars with constant workability) as follows:

40

20

0 0

5

10

15

20

25

30

Limestone content (%) Fig. 8. Compressive strength of mortars (W/C = 0.5).

35

1151

A. Marzouki et al. / Construction and Building Materials 48 (2013) 1145–1155 Table 9 Tensile and compressive strength of constant workability mortars. Tensile strength (MPa)

C0 C5L C12L C20L C25L C30L C35L

Compressive strength (MPa)

2d

7d

28d

90d

360d

2d

7d

28d

90d

360d

4.0 2.4 4.1 2.7 3.5 3.0 2.9

6.7 5.3 6.2 4.6 6.3 4.9 4.9

8.7 7.4 8.5 7.0 8.4 6.6 6.6

9.8 9.0 9.1 8.3 9.3 7.4 7.1

10.6 9.9 10.3 8.7 10.3 7.8 7.5

16.5 11.1 16.5 11.7 16.7 12.6 13.2

28.4 23.4 27.9 22.0 29.0 21.6 21.3

47.1 33.3 39.5 36.5 40.6 27.1 28.7

53.1 42.4 45.1 43.1 45.3 36.4 35.3

55.9 55.8 57.6 50.1 50.4 41.6 40.2

content) does not compensate for poor grinding (C5L). Finer grinding (C25L) is equivalent to or more beneficial than supplementary fillers (C30L and C35L) or a higher clinker proportion (the other cements). The grinding quality and the fineness of clinker and fillers are thus parameters which have complementary roles. At medium ages (28 days, Fig. 9b), the grinding effect lessens, as does the influence of the filler amount, since experimental and theoretical strengths become closer (with the exception of the less well-ground cement). Over longer time periods (90 days and 1 year, Fig. 9b), fillers become again more interesting, especially for the higher content, irrespective of the grinding quality. The binding effect associated with the formation of carboaluminates (undoubtedly coming from the hydration of coarser grains of clinker) can explain this behavior. In the literature, the results of some works can be compared to those in this study. For example, Vuk et al. [11] have made standardized mortars with cement containing 0% and 5% of limestone addition. These cements were manufactured from two clinkers having a finer and a coarser fineness. The compressive strengths obtained at younger ages (2 and 7 days) show that cement with 5% of limestone is better than the cement without limestone addition, while at 28 days the opposite occurs. Tsivilis et al. [10] compared cement pastes with various percentages of limestone addition (0–35%) and increasing fineness with this addition, ranging from 300 to 500 m2/kg. Their results show that the addition of 5% of limestone represents the optimum strength. For the other additions, strengths decrease, in particular at 28 days. Nehdi et al. [28] showed that at 3 days, the compressive strength is little affected by the substitution of 10% and 15% of cement by limestone while it decreases significantly for higher limestone content. Measurements carried out on these mortars have also allowed research to show a correlation between tensile strength and compressive strength (Fig. 10). A power law fit to the overall results is

60

Effect on strength (%)

2 days

C25L

7 days

40

C35L C12L

20

C30L C0

0 1

10

100

C20L -20

-40

C5L Grinding quality

Fig. 9a. Effect of grinding quality and rates on filler strength at 2 and 7 days.

60 28 days

Effect on strength (%)

Cement

90 days

40

360 days

C25L C12L

20

C35L C30L C0

C20L

0 1

10

100

-20

C5L -40

Grinding quality

Fig. 9b. Effect of grinding quality and filler rates on strength at 28, 90 and 360 days.

satisfactory, as often reported in the literature [33,34]. It is given as follows: 0:85

ft ¼ 0:34ðfc Þ

ð9Þ

The results are more spread out when performance increases, thus reflecting a more marked effect at later ages of the limestone filler amount and the grinding quality. However, it is generally noted that the cement-based mortars with limestone additions behave similarly to those without. The possibility of improving strength by a finer grinding of clinker is confirmed by this research. In the presence of limestone, the simultaneous grinding of all components leads, however, to an increase in the fineness of the calcium carbonate fraction of the mixture, which has the effect of accelerating the increase in strength and provides a significant binding effect at later ages. The effect of air exposure (airing) was also appreciated. For this purpose, a sample of each type of cement was spread over a PVC plate (thin and regular layer) and exposed at room temperature (in front of a window) for 1 week. In each case, two sets of 4  4  16 specimens of mortars were prepared with constant workability containing either cements exposed to air or cements stored in airtight bags. The performances of the specimens were measured after 28 days of water curing. The results are shown in Fig. 11. Those obtained with cements stored in bags confirm both the values obtained previously (28 days, Fig. 8) and the good reproducibility of the tests. Conversely, the performances obtained with cements exposed to air are always inferior, in particular for cement C0 without limestone fillers. The relative decrease in compressive strength for this cement reaches 20% and is lower for the other cements (4% C25L). It can be inferred that the limestone fillers minimize the effects of exposure to air, although they increase powder porosity (see Table 8). It would appear that their greater fineness results in a less permeable packing and affords a certain degree of protection to the clinker grains with respect to hydration and early carbonation.

1152

A. Marzouki et al. / Construction and Building Materials 48 (2013) 1145–1155 Table 10 Cement categories according to standard NT 47.01 [5], from mechanical tests on mortars with W/C = 0.5.

12 y = 0,34x

0,85

2

Tensile stength (MPa)

R = 0,98

Cement

9

C0 C5L C12L C20L C25L C30L C35L

6

W/C=0.50

3

Compressive strength (MPa)

Constant workability Fitting

Category

2 days

7 days

28 days

16.5 9.5 16.5 12.1 16.6 13.4 13.9

28.4 21.9 26.9 22.5 28.2 22.6 22.0

47.1 30.7 37.7 37.0 40.8 31.4 31.0

CEM NC CEM CEM CEM NC NC

I 32.5 R II/A-L 32.5 R II/A-L 32.5 R II/B-L 32.5 R

N: normal early strength; R: rapid early strength; NC: not classified.

0 0

20

40

60

Compressive strength (MPa) Fig. 10. Correlation between tensile and compressive strength.

Finally, the mechanical tests carried out on mortars with W/C = 0.50 allow the cements studied to be classified according to the following standard categories (Table 10): – CEM I 32.5 R for C0, – CEM II/A-L 32.5 R for C12L and C20L, – CEM II/B-L 32.5 R for C25L. Cements C5L, C30L and C35L are not classified due to their lower performances. However, they may fall into the category of masonry cements as they satisfy the conditions required of initial setting time, SO3 content and strength at 7 and 28 days. 3.4. Dimensional stability The measurements of dry shrinkage and expansion under water on mortar specimens equipped with stainless pins lasted 2.5 years. The initial length l0 was measured after demolding at 24 h. The samples for the measurement of dry shrinkage were exposed in a closed and not controlled room (temperature 20 °C, relative humidity 60%). Those used for the measurement of the expansion were cured in a water tank placed in the same room. The results are presented in Figs. 12a and 12b. Dry shrinkages are initially rapid (300 lm/m at 28 days). After, it slows down to reach values of about 750 lm/m after 1 year (Fig. 12a). The initial values which are rather low and the general fluctuations observed are attributed to climatic conditions and variations in the curing room between the winter and summer

periods. The limestone fillers content in cement has no real influence except at 7 days (Fig. 12b) where the dry shrinkage is more substantial when the fillers content and/or the finer grinding are high. The acceleration in hydration (see previously), which induces autogenous shrinkage at early age, is probably the cause of this increase. This trend is less pronounced over longer time periods where the dry shrinkages are essentially equivalent regardless of the limestone filler ratio in the cement. Expansion under water is low after the first three months and then increases, in particular for the reference cement without limestone fillers C0 (Fig. 12a). A shrinkage phase appears after 1 year for cements with limestone filler. It becomes more significant when the filler content and/or the fine grinding of cement are higher. For high contents of limestone fillers, shrinkage ends up cancelling the expansion recorded previously, by creating a further shrinkage compared to the initial stage. It should be noted that a similar phenomenon occurred in tests carried out in parallel on concretes (results not presented here). The origin of this effect is probably due to the modification of permeability and capillary internal tensions [32] induced by the evolution of the cement paste porosity associated with the presence of fillers as well as calcium carboaluminate hydrates. The total dimensional variations (sum of dry shrinkage and expansion under water) increase up to one year, regardless of the amount of limestone fillers. At 2.5 years, they reach 1200 lm/m for the reference mortar without limestone fillers (cement C0). On the other hand, they halve with cement C35L, due to the shrinkage under water which was previously noted. The amount of limestone fillers in cement and/or the finer grinding do not have particularly harmful consequences on the dimensional stability. With higher content, the fillers even have a beneficial effect because of shrinkages observed under water.

age (days)

60 0

Cement exposed one week on air

MPa

40

Compressive stength 20

Tensile stength 0 0

5

10

15

20

25

30

35

Limestone content (%) Fig. 11. Mechanical strength of cements after 1 week of exposure to air.

Shrinkage and expansion (µm/m)

Cement kept from air

300

600

900

600 400

in water

200 0

C0 C12L C25L C35L

-200 -400 -600 -800

C5L C20L C30L

in air

-1000 Fig. 12a. Shrinkage and expansion of mortars (constant workability).

1153

A. Marzouki et al. / Construction and Building Materials 48 (2013) 1145–1155

20

Fillers content (%) 0

5

10

15

20

25

30

35 19

in water

Shrinkage (µm/m)

400 200 0 -200 -400 -600 -800

7 days 28 days 90 days 360 days 880 days

Water porosity (%)

600

18 17 16 15 14 0

in air

5

10

15

20

25

30

35

Limestone content (%)

-1000 Fig. 13a. Water porosity at 7-day old mortars (W/C = 0.5). Fig. 12b. Variation of shrinkage as a function of limestone mass percentage.

20

3.5. Porosity and capillary absorption

1 Here we neglect the Le Chatelier contraction. Similarly, while having maintained a constant mass of binder (i.e., 450 g), the binder volume increases with the filler content due to the decrease in its density. The mortar volume then also increases. These volumes changes were taken into account in the calculations.

19

Water porosity (%)

The water porosity of mortars with constant ratio W/C = 0.5 is measured after 7 days of curing in water and shown in Fig. 13a. The measurement was carried out on specimens of approximately 2  4  4 cm3 by hydrostatic weighing, in accordance with EN 1936, after drying in a ventilated oven at 45 °C until constant mass. This porosity increases along with the amount of limestone fillers present in the cement, increasing from 14.5% (C0) to 16.5% (C30L). Since the amount of trapped air is quasi-constant (Fig. 5) and the mass of the constituents is identical for all the mortars, the increase in porosity can be attributed to: (i) the decrease of clinker proportion (ii) the grinding quality. With regards to the first point, it should be noted that clinker substitution by limestone fillers requires a lower consumption of water hydration, and therefore, under test conditions, an increase porosity of the composite. From a formal point of view, and to a first approximation, we can consider that the measured porosity is, therefore, equivalent to the addition of free water (residual water) and entrapped1 air (Fig. 5). Free water is equal to the process water, minus water combined with hydrates (combined water and water of porosity). Considering a ratio W/C = 0.266 to estimate the water consumed by the hydrates – a realistic value [35] if we take into account notably the mortar age – then, we find the same porosity of reference mortar, which not contain limestone fillers (C0). However, applying this ratio to the other mortars leads to theoretical porosities which are much higher than those measured (see Fig. 13b, white marker points). Conversely, the measured porosities are found only by considering a higher hydration ratio, increasing to 0.373. These values seem less likely [35], even when a weighting linked to an accelerating effect at early age of limestone fillers is taken into account. The porosity of mortars with fillers can be explained by another phenomenon minimizing the porosity of the binding phase, namely grinding quality. This hypothesis refers to tests on normal paste (see Table 8 and Fig. 3) where it was shown that finer grinding of cements led to increased water demand and, therefore, a higher porosity (see § 3.1). If the water quantity brought to the pastes is lower, their porosity will be reduced. This is what occurs in the mortars with W/C = 0.50 where the same quantity of water is used, whatever the compacted characteristics of cement. In a mor-

Hydration only + grinding quality Egality

18 17 16 15 14 14

15

16

17

18

19

20

Theorical porosities (%) Fig. 13b. Comparison between experimental and theoretical porosities calculated by taking into account the hydration and the grinding quality of cement (mortars with W/C = 0.5).

tar where cement is compacted only a little (finer grinding), the binding phase porosity (paste) is lower than a mortar where the cement is more compacted (coarser grinding). It is noted that these differences in porosity should lead to different rheological behaviors. However, they were not actually detected (see Table 8), probably because the apparatus used is less sensitive. The porosity deficit compared to the reference value is equal, to a first approximation, to the difference between the porosity of the mortar paste under consideration and that of the reference mortar. These porosities were calculated using a model to which adjustments had been made to take into account the results of consistency tests carried out on normal paste versus grinding quality (image smoothing in Fig. 3). They were then multiplied by a reduction coefficient quite simply equal to the ratio between the paste porosity of the reference mortar and the porosity of the normal reference paste (C0). The paste porosity of reference mortar is deduced from the mortar’s composition. The results obtained are presented in Fig. 13b (black marker points). They show that the measured porosity can therefore be satisfactorily predicted by these calculations when the grinding quality is explicitly taken into account. Water absorption tests by capillarity suction were carried out on constant workability mortars cured in water for 28 days and then in air until constant mass (60 days). A sealed epoxy resin was applied to the four sides so that only unidirectional absorption is possible. According to the protocol, the curves of cumulative

A. Marzouki et al. / Construction and Building Materials 48 (2013) 1145–1155

2

capillary absorption (Kg/m )

1154

6

4

C0 C5L C12L C20L C25L C30L C35L

2

0 2

10

18

26

square root of time (min

34

42

0.5

)

Fig. 14a. Capillary water absorption.

16

2

Capillary parameters

R = 0,67

12

Sorptivity 8

kg/m2 after 24 h

C20L

C35L C25L C30L

4

2

R = 0,66

C5L C0 C12L

accelerate the setting, especially as the cement is ground more finely. They contribute to strength by the formation of hemicarboaluminate at early ages, monocarboaluminate over longer periods, without modifying the mechanical behavior or compressive/tensile strength. Their presence allows a decrease in the heat of release. They have little influence on dimensional stability and even improved it under water. They reduce porosity at the expense of capillarity and sorptivity. Grinding quality appears as a crucial parameter in the control of these properties. It particularly affects clinker fineness because limestone is softer and always better pulverized. The limestone fillers therefore reduce powder compactness, due to an overabundance of the finest sections, which interfere with each other and with the finer clinker grains. Grinding quality also affects performance. If it is poor, the strengths are largely affected even in the presence of a small amount of fillers. On the other hand, a finer grinding does not offset the presence of higher filler content. This study has not dealt with the influence of other parameters on the cements’ composition. These parameters include the amount and variety of aluminous phases at the origin of carboaluminate formation, the amount and nature of sulfates, the presence of plasticizer, and the role of limestone fillers with respect to durability (freezing, carbonation, sulfate attack, chloride diffusivity, etc.). However, it shows that from an ordinary Portland clinker, Portland-limestone cements containing up to 25% of fillers can perform almost identically to the original Portland clinker over time, if a sufficient or optimized grinding is carried out. Under these conditions, the Portland-limestone cements can be used in many civil engineering applications, thus allowing substantial economies of a financial and environmental nature to be made. This is particularly true in Tunisia where limestone resources are abundant. Acknowledgements

0 1

10

100

Grinding quality Fig. 14b. Capillary parameters.

mass gain per unit area of the inflow surface were shown as a function of the square root of time (Fig. 14a). Two phases appear which correspond, in theory, to the filling of two capillary systems [34]. The experimental curves show a clear influence of the presence/ fineness of limestone fillers and/or porosity, since the rate of absorption – or sorptivity – and the amount of water absorbed varies with these parameters. Thus (Fig. 14b), mortar with the reference cement (C0) presents the lowest absorption and sorptivity whilst mortar with the finest grinding cement (C30L) presents the highest. A fine grinding of fillers (Table 7) clearly favors the capillary rise, that is, the presence of smaller and finer pores [36].

4. Conclusions This study was performed with seven Tunisian cements manufactured on an industrial scale by the intergrinding of clinker, natural gypsum and limestone indifferent ratios. Their manufacture did not lead to the expected regularity, in particular in terms of grinding quality. This ‘‘error’’, however, has allowed the importance of this parameter to be highlighted with respect to most of the analyzed properties. It is noteworthy that, with respect to powder compactness (powder packing density) and paste consistency, the limestone fillers behave in a similar physical way than ground clinker. They

The authors would like to thank the managers and technicians of the Gabès Cement Company of Tunisia which manufactured cements for this study on an industrial scale. They also acknowledge the contribution of Mr. Christopher Butler for help in improving the English language of the article. References [1] Ingram Kevin D, Daugherty Kenneth E. A review of limestone additions to Portland cement and concrete. Cem Concr Compos 1991;13:165–70. [2] Cement Association of Canada. ; 2011. [3] Survey with Tunisian cement-manufacturers. Personal Communication; 2010. [4] Internal reports of the Ministry of Industry and Technology-Tunisia; 2011. [5] Tunisian Standards: NT 47.01 – Partie 1: composition, spécification et critère de conformité des ciments courants; 2007, I.N.NOR.P.I, [in French]. [6] Ministère de l’Equipement de la Tunisie, cahiers des charges des projets publics et privés; 2010–2011. Personal Communication. [7] Journal Officiel de la République Algérienne N°40 (in French) – 2 Juillet; 2003. p. 18. [8] Cembureau. ; 2011. [9] Tsivilis S, Chaniotakis E, Kakali G, Batis G. An analysis of the properties of Portland limestone cements and concrete. Cem Concr Compos 2002;24:371–8. [10] Tsivilis S, Batis G, Chaniotakis E, Grigoriadis Gr, Theodossis D. Properties and behavior of limestone cement concrete and mortar. Cem Concr Res 2000;30:1679–83. [11] Vuk T, Tinta V, GabrovsÏek R, KaucÏicÏ V. The effects of limestone addition, clinker type and fineness on properties of Portland cement. Cem Concr Res 2001;31:135–9. [12] Bobrowski GS, Wilson JL, Daugherty KE. Limestone substitutes for gypsum as a cement ingredient. Rock Prod 1977;8(2):64–7. [13] Adams LD, Race RM. Effect of limestone addition upon drying shrinkage of Portland cement mortar. In: Klieger P, Hooten RD, editors. Carbonate addition to cement, ASTM STP 1064. Philadelphia, PA: American Society for testing and materials; 1990. p. 41–50. [14] Mayfield LL. Limestone addition to Portland cement – an old controversy revisited. Cem, Concr Aggr 1988;10(1):3–8.

A. Marzouki et al. / Construction and Building Materials 48 (2013) 1145–1155 [15] Bonavetti V, Donza H, Rahhal V, Irassar E. Influence of initial curing on the properties of concrete containing limestone blended cement. Cem Concr Res 2000;30:703–8. [16] Taylor HFW. Cement chemistry. Academic press; 1997. p. 475. [17] ASTM C188-09: Standard Test Method for Density of Hydraulic Cement. [18] Pliskin L. La fabrication du ciment, Edition Eyrolles; 1993, ISBN:2-212-011962. [in French]. [19] Ellerbrock HG, Sprung S, Kuhlmann K. Effect of interground additives on the properties of cement. Zem-Kalk-Gips, Edition B 1985;38(10):586–8. [20] Bouasker M, Mounanga P, Turcry P, Loukili A, Khelidj A. Chemical shrinkage of cement pastes and mortars at very early age: effect of limestone filler and granular inclusions. Cem Concr Compos 2008;30:13–22. [21] Chloup Bondant M, Evrard O. Tricalcium aluminate and silicate hydration. Effect of limestone and calcium sulfate. In: Colombet P, editor. Proceedings of the 2nd international conference on nuclear magnetic resonance spectroscopy of cement-based materials. Berlin: Springer Verlag; 1998. p. 295–308. [22] Bentz DP. Modelling the influence of limestone filler on cement hydration using CEMHYD 3D. Cem Concr Compos 2006;28(2):124–9. [23] Bonavetti VL, Rahhal VF, Irassar EF. Studies on the carboaluminate formation in limestone filler-blended cement. Cem Concr Res 2001;31:853–9. [24] Feldman RF, Ramachandran VS, Sedra PJ. Influence of CaCO3 on the hydration of C3A. J Am Ceram Soc 1965;48(1):25–30. [25] Vernet C, Noworyta G. Mechanisms of limestone reactions in the system (C3A– CaSO4H2O–CH–CaCO3–H): competition between calcium monocarbo- and monosulfo-aluminate hydrates formation. In: Proc Int Congr Chem Cem, 9th, vol. IV, New Delhy, India; 1992. [26] Ramachandran V, Zhang C. Influence of CaCO3 on hydration and microstuctural characteristics of tricalcium silicate, II Cemento. 1986;83(3):129–52.

1155

[27] Husson S, Guilhot B, Pera J. Influence of different fillers on the hydration of CaCO3. In: Proc Int Congr Chem Cem, 9th, vol. IV, New Delhy, India; 1992. p. 83–89. [28] Nehdi M, Mindess S, Aïtcin P-C. Optimization of high strength limestone filler cement mortars. Cem Concr Res 1996;26(6):883–93. [29] NF P 18-452: Mesure du temps d’écoulement des bétons et des mortiers aux maniabilimètres; 1988. [30] Benachour Y, Davy CA, Skoczylas F, Houari H. Effect of a high calcite filler addition upon microstructural, mechanical, shrinkage and transport properties of a mortar. Cem Concr Res 2008;38:727–36. [31] Bédérina M, Khenfer MM, Dheilly RM, Quéneudec M. Reuse of local sand: effect of limestone filler proportion on the rheological and mechanical properties of different sand concretes. Cem Concr Res 2005;35:1172–9. [32] Pipilikaki P, Beazi-Katsioti M. The assessment of porosity and pore size distribution of limestone Portland cement pastes. Constr Build Mater 2009;23:1966–70. [33] Ghrici M, Kenai S, Said-Mansour M. Mechanical properties and durability of mortar and concrete containing natural pozzolana and limestone blended cements. Cem Concr Compos 2007;29:542–9. [34] Neville MA. Properties of concrete. England: Addison Wesley Longman; 1996. [35] Mounanga P. Étude expérimentale du comportement de pâtes de ciment au très jeune âge: hydratation, retraits, propriétés thermo-physiques, PhD thesis. Nantes: Université de Nantes; 2003 [in French]. p. 72. [36] Bessa-Badreddine A. Etude de la contribution des additions minérales aux propriétés physiques, mécaniques et de durabilité des mortiers, PhD thesis. France: Université de Cergy Pontoise; 2004 [in French].