Construction and Building Materials 38 (2013) 101–109
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Mechanical, microstructure and rheological characteristics of high performance self-compacting cement pastes and concrete containing ground clay bricks Mohamed Heikal a,⇑, K.M. Zohdy b, M. Abdelkreem b a b
Chemistry Department, Faculty of Science, Benha University, Benha, Egypt Higher Technological Institute, 10th of Ramadan City, Egypt
h i g h l i g h t s " Presence of SCC admixture, strength of concrete increases up to 28 days. " Increase of powder content of GCB, the compressive strength of concrete increases. " Pastes made with 12.5% and 37.5% GCB show higher strength with SCC at 28–1095 days. " Increase of GCB content increases the shear stresses values in cement pastes. " The microstructure of GCB–OPC displayed a more dense arrangement, enhances the compressive strength.
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Article history: Received 30 April 2012 Received in revised form 8 July 2012 Accepted 22 July 2012 Available online 21 September 2012 Keywords: Self-compacting concrete Compressive strength Rheology Microstructure
a b s t r a c t The work aimed to utilize ground clay bricks (GCBs) in the production of self-compacting concrete. Physico-mechanical, rheological and microstructure of cement pastes and concrete were investigated. Total powder contents were 400 kg/m3, the cement was replaced by GCB by 0.0, 50, 100 and 150 kg/m3. The compressive strength of concrete decreased with GCB content in the absence of self-compacting concrete (SCC) admixture, whereas, increases in the presence of SCC admixture up to 28 days. Increase of GCB content up to 250 kg/m3, the compressive strength of concrete increases. GCB enhances the compressive strength due to the pozzolanic reaction to produce additional CSH, which precipitated in some open pores. The compressive strength of OPC pastes increase with SCC admixture up to 1.5 mass%, whereas decreases with SCC admixture up to 2 mass%. On the other hand, cement pastes made with 12.5% and 37.5% GCB in the expanse of OPC cement show higher compressive strength with SCC admixture at 28–1095 days. The efficiency of SCC admixture decreases as GCB content increases up to 12.5%, whereas the efficiency increases with GCB content up to 37.5%. The presence of SCC superplasticizer, the microstructure displayed a more dense arrangement of microcrystalline C–S–H as the main hydration products with sheets of Ca(OH)2 as shown in the micrograph. Useful conclusions and recommendations concerning use of 30–40 mass% of GCB in self-compacting concrete. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction Self-compacting concrete (SCC) is considered as a concrete that compacted under self-weight with little or no vibration effort and cohesive enough to be handled without segregation or bleeding. SCC used to facilitate and ensure proper filling and good structural performance of restricted areas and heavily reinforced structural [1,2]. So, SCC has been increasingly used in concrete construction. The principal reasons for the growing interest is because of the ease in placement in heavily reinforced areas which are otherwise
⇑ Corresponding author. Tel.: +20 1003598184; fax: +20 133222578. E-mail address:
[email protected] (M. Heikal). 0950-0618/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.conbuildmat.2012.07.114
difficult to access, the reduced effort in accomplishing some of the casting tasks and the significant reduction of the construction period. Additionally, the technology has improved the performance in terms of hardened material properties such as strength, durability, and surface quality [3]. SCC has many technical, social, and overall economical advantages; however its cost could be 2–3 times than normal concrete. To reduce the cost of SCC use of mineral admixtures such as fly ash, limestone filler, ground clay bricks (GCBs) and blast-furnace slag could be used to increase the slump of the concrete mix as well as improve the mechanical properties and durability of concrete. The incorporation of fly ash also reduces the need for viscosity modifying chemical admixtures and reduces cracking of concrete due to the low heat of hydration heat of hydration of the cement
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[4–8]. The excellent workability and flowability of super-flowing concrete containing 30–40% fly ash by weight of the total cementitious materials were reported [9,10]. Blended materials used in SCC with binary and ternary binder systems having complex hydration mechanisms. It has been shown that particle size, shape, morphology and internal porosity of secondary raw materials all have a very significant effect on the overall response of self-compacting systems [11]. This response is improved in the presence of limestone powder or fly ash with either silica fume or amorphous rice husk ash [12]. Hydration reaction of self-consolidating concrete gets accelerated and modified due to improved nucleation possibilities while the presence of fly ash makes interference in cement hydration and changes reaction kinetics in the sense that fly ashes tend to lengthen the dormant period [13]. The effect of blast-furnace slag and two types of superplasticizers namely, polycarboxylate and naphthalene sulphonate formaldehyde superplasticizers on the properties of SCC were discussed [14]. The results showed that polycarboxylate superplasticizer concrete mixes give more workability and higher compressive strength than those with naphthalene sulphonate superplasticizer. In cementitious systems, hydration reactions can perturb the behavior of suspensions [15,16]. Dispersion of agglomerated cement particles is recognized to constitute the main method by which superplasticizers improve the workability of concrete without increasing the water content. Dispersion forces, referred to as Van der Waals forces, are the main cause for agglomeration of cement particles in concrete and of the poor resulting flow properties. To counter these forces and improve flow of SCC, dispersants are added. Understanding these effects is a key aspect for predicting which combinations of cement and superplasticizers will lead to best workability [17]. Important factors are the length of graft chains, degree of polymerization, and the density of graft chains. The characteristics of superplasticizers depend on the raw materials and the synthesis conditions [17,18]. The fluidity of cement pastes containing naphthalene sulphonate depends on the molecular weight. Furthermore the retardation effect depends on its concentration and C3A content of the cement. The operative mechanism of polycarboxylic ether type owing to electrostatic repulsive forces is based on the negative charge of polycarboxylate and steric repulsive forces on the cement particles based on long side strains. The mechanism of action of naphthalene sulphonate based superplasticizer is different from the one of a polycarboxylate superplasticizer. The first one acts by electrostatic repulsion, and the second one acts by steric hindrance effect [19]. Since cement is the most expensive component of concrete, reducing cement content is an economical solution. Mineral admixtures can improve particle packing and decrease the permeability of concrete. Besides the economical benefits, such uses of by-products or waste materials in concrete reduce environmental pollution. Therefore, the durability of concrete is also increased [20–25]. The development of SCC is considered as a milestone achievement in concrete technology due to several advantages. Self-compactable the fresh concrete must show high fluidity besides good cohesiveness [26]. One of the disadvantages of SCC is its cost, associated with the use of chemical admixtures and use of high volumes of Portland cement. One alternative to reduce the cost of SCC is the utilization of mineral admixtures [27–30]. In addition, the incorporation of these fine materials can enhance the grain size distribution and the particle packing, thus ensuring greater cohesiveness [30,31]. The present work aimed to utilize Homra, which is the crushed portion of ground clay bricks (GCBs) from the Misr Brick (Helwan, Egypt) to produced self-compacting concrete. The physicomechanical, rheological and microstructure of cement pastes and concrete were investigated.
2. Experimental technique 2.1. Materials 2.1.1. Cement Ordinary Portland Cement (OPC) is used in all test specimens, the tests carried out on the used cement to determine its physical properties according Egyptian Code of Practice [32]. The chemical analysis of material was given in Table 1.
2.1.2. Ground clay bricks A ground clay brick (Homra; GCB) is a solid waste materials produced from the manufacture of clay bricks. These crushed portions of Homra are not of commercial use and even may be considered as a solid waste to the environment. The mineralogical composition of the ground clay bricks is seen from the XRD pattern in Fig. 1. The ground clay bricks sample constitutes mainly of SiO2, Al2O3, Fe2O3, CaO, SO3, MgO, and Na2O, K2O as traces and chemical properties were given in Tables 1. GCB sample constitutes mainly of free silica quartz from added sand and from clays and amorphous aluminosilicate from the decomposition of clay minerals as well as albite and hematite.
2.1.3. Aggregates Locally available continuously graded crushed dolomite aggregates (magnesium carbonate and calcium carbonate) with a normal maximum size of 20 mm and well graded natural sand free from impurities with a fineness modulus of 2.75 were employed. The relative density of the coarse aggregate and sand were 2.66 and 2.56 and their absorption rates were 1.9% and 1% respectively.
2.1.4. Admixtures In this study, polycarboxylate self-compacting admixture is used to increase the flow capability of the concrete and improve the viscosity. It is turbid liquid, with a specific gravity of 1.11 and pH value was 8.0 ± 0.5. The used dosages of polycarboxylate self-compacting admixture were 0.0, 0.5, 1.0, 1.5 and 2.0 mass% of concrete.
2.2. Mix proportions Fifteen concrete mixes were made, which had total powder content of 400, 500 and 600 kg/m3 (cement and ground clay bricks), coarse aggregate, fine aggregate content w/p ratio and polycarboxylic ether based superplasticizer (Viscocret 5400) were given in Table 2. The cement was replaced by ground clay bricks as shown in Table 2.
2.3. Mixing and casting For these mix proportions, required quantities of materials were weighed. Cement and GCB were mixed in dry state as well as coarse and fine aggregates were mixed dry separately. After adding water, all materials were mixed together to obtain the homogeneous mix. The casting of the mixes was done immediately. After casting, test specimens were left in the casting room for 24 h at a temperature of about 20 °C ± 0.5, in 100% relative humidity. The specimens were removed from mold after 24 h, and then immersed in water-curing tank until the time of the test. The cubes of size 150 150 150 mm were cast for determination of compressive strength after 28 days. For pastes specimens, OPC has been partially substituted by GCB with ratio of 0, 12.5 and 37.5 mass%. The ingredients of each mix were blended in a porcelain ball mill for 1 h using a mechanical roller mill to ensure complete homogeneity. The superplasticizer was added in different amounts to the mixing water. The solid mix of each paste was mixed with a sufficient amount of water to form a paste of standard consistency according to ASTM specifications [33]. The pastes were molded in 2 2 2 cm cubes for studying compressive strength and scanning electron microscopy.
Table 1 Chemical oxide composition of the starting materials mass%. Oxides
OPC
GCB
SiO2 Al2O3 Fe2O3 CaO MgO Na2O K2O SO3 L.O.I
20.39 5.60 3.43 63.07 2.91 0.38 0.35 2.42 3.21
75.06 14.25 5.61 1.30 1.35 0.19 0.08 0.70 0.00
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Fig. 1. XRD patterns of GCB. The hydration of cement pastes were stopped by pulverizing 10 g of representative sample in a beaker containing methanol–acetone mixture (1:1), then mechanically stirred for 1 h. The mixture was filtered through a gooch crucible, G4 and washed several times with the stopping solution then with ether. The solid was dried at 70 °C for 0.5 h complete evaporation of alcohol then collected in polyethylene bags; sealed and stored in desiccators for analysis [17]. 2.4. Rheological measurements Different mixes of polycarboxylate self-compacting admixture/GCB/cement were prepared at constant W/C powder ratio 0.35. The mixes were stirred by mixer about 120 rpm for 3 min, 1 min rest and other one by the above speed. Exactly 50 g of each mix was transport to the Rheotest cell as described in an earlier publication [34]; the ratio of radii of measuring tube and measuring cylinder (R/r) was 1.24. The test begins exactly after 6.5 min from contact of cement and water including the stirring time. The shear rate was measured in the range from 3 up to 146 s 1. 2.5. Microstructure The microstructure of the selected samples was examined using the scanning electron microscopy JEOL-JXA-840 (high-resolution imaging at up to 100,000).
3. Results and discussion 3.1. Compressive strength determination Compressive strength test results for concrete mixes with polycarboxylate self-compacting admixture were given in Fig. 2. Total powder content of 400 kg/m3 (cement and ground clay bricks), the cement were replaced by GCB by 0.0, 12.5, 25 and 37.5 mass% (i.e. 0.0, 50, 100 and 150 kg/m3). When the strengths are compared within each respective curing regime, the strength decreased with increasing GCB content. The loss of strength could be attributed to the weak adhesion between the interface between the aggregates and the cement pastes [35].
With the increase of superplasticizer dosages the compressive strength increases (Fig. 2). When compared to the control mixture, increasing the amounts of GCB content the compressive strength decreases. Here, the role of GCB is also better understood as it acts as filler-pozzolanic mineral admixture reducing the compressive strength. But, it has shown the best performance at 28 days, due to the physical nature of better packing, as addition of GCB governs the compressive strength due to the denser matrix and the better dispersion of cement grains [36]. Furthermore, GCB acts as nucleation sites for the early reaction products of CH and CSH, which accelerates the hydration of cement clinkers (especially C3S) and consequently increase the compressive strength [37,38]. GCB is finer material than OPC. The effect of nucleation on the strength is dependent on the mineral admixture’s affinity to cement hydrates, and it increases with fineness and specific surface area of the mineral admixture. This reaction accelerates the hydration and increases the compressive strength. The same effect on compressive strength has been observed with natural pozzolana and cement was replaced from 10% up to 25% of blast furnace slag [14,39,40]. Fig. 3 represented the effect of the different powder content of GCB on compressive strength of self-compacting concrete made with 2% self-compacting admixture cured under tap water at 28 days. The content of GCB increases from 50, 150, 200 and 250 kg/m3, the total powder contents become 400, 500, 550 and 600 kg/m3. Increase of the GCB content up to 250 kg/m3, the compressive strength of testing concrete increases. GCB enhances the compressive strength due to the pozzolanic reaction of GCB with liberated lime from the hydration of OPC phases to produce the additional hydration products, which precipitated in some open pores, hence the porosity decreases and bulk density increases. The reduction of the porosity affects on the efficiency of pozzolanic reaction via approaching the grains of GCB from liberated lime to form additional amounts of calcium silicates hydrates CSH. These additional hydrates deposit in the available pores leading to closed compact structure. The increased total powder content improves the physical packing of aggregates and produces a greater amount of calcium silicate hydrate (CSH) leading to a higher compressive strength [41]. Figs. 4–6 show the compressive strength data of cement pastes cured under tap water up to 1095 days in the presence of different dosages of self-compacting admixture up to 2 mass%. As expected, the compressive strength increased with age. The rate of increase depended upon the level of cement replacement and age. Fig. 4 represented the variations of compressive strength of OPC pastes in the presence of different dosages of SCC admixture. The results show that the compressive strength of all cement pastes increases
Table 2 Mixture proportions of self-compacting concrete, kg/m3. Mix no.
OPC
GCB
Sand
Coarse aggregate
Water
w/p
W/C
Total powder content
Superplasticizer (%)
M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M11 M12 M13 M14 M15
400 400 400 350 350 350 300 300 300 250 250 250 350 350 350
– – – 50 50 50 100 100 100 150 150 150 150 200 250
900 900 900 900 900 900 900 900 900 900 900 900 900 900 900
800 800 800 800 800 800 800 800 800 800 800 800 800 800 800
200 200 200 200 200 200 200 200 200 200 200 200 250 275 300
0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
0.50 0.50 0.50 0.57 0.57 0.57 0.67 0.67 0.67 0.80 0.80 0.80 0.714 0.79 0.85
400 400 400 400 400 400 400 400 400 400 400 400 500 550 600
1.0 1.5 2.0 1.0 1.5 2.0 1.0 1.5 2.0 1.0 1.5 2.0
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Fig. 2. Compressive strength of self-compacting concrete made with GCB in expense of OPC and self-compacting admixture cured at 28 days.
Compressive strength, kg/cm2
300
280
260
240 GCB content
220 0
50
100
150
200
250
GCB content, kg/m3 Fig. 3. Compressive strength of SCC made with different powder content up to 600 kg/m3 cured at 28 days.
with curing time. The compressive strength of cements pastes increase with SCC admixture up to 1.5 mass%. Increase the dosage of SCC admixture up to 2 mass% the compressive strength decreases up to 1095 days. SCC admixture (polycarboxylate based superplasticizers) interacts with Ca2+ ions and, a chelating is formed in pastes as a result a lower Ca2+ concentration, thus hindered the solid phase nucleation, hydration products growth and retard cement hydration [42]. Figs. 5 and 6 represented the variations of compressive strength of OPC pastes containing 12.5 and 37.5 mass% GCB. The decrease in the early strength (at 7 days) is directly dependent on the amount of cement replacement by GCB and dosage of SCC superplasticizer. The pastes made with 12.5% and 37.5% GCB in the expanse of OPC cement show the strength values of 344 and 268 kg/cm2 even at the age of 7 days in the absence the self-compacting admixture. This pastes achieved higher compressive strength than the control concrete mixture at the age of 366 and 1095 days as well as in the presence of SCC admixture up to 1.5%. Pastes containing 37.5 mass% of GCB in the presence of 2% SCC admixture showed a higher compressive strength values at 1095 days than control mix (0.0% SCC admixture). In general, SCC mixtures containing
Fig. 4. Compressive strength of cement pastes made with OPC and different dosages of SCC admixture up to 1095 days.
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Fig. 5. Compressive strength of cement pastes made with OPC + 12.5% GCB in presence of different dosages of SCC admixture up to 1095 days.
Fig. 6. Compressive strength of cement pastes made with OPC + 37.5% GCB in presence of different dosages of SCC admixture up to 1095 days.
1500 OPC 12.5% GCB
1200
Shear stress, Pa
0%, 12.5% and 37.5% GCB developed high compressive strength in the range of 1100, 1320 and 1314 kg/cm2 at 1095 days. This may be explained by the increased particle packing and chemical activity (pozzolanic activity). SCC admixture improves the microstructure of the cement pastes forming the close compact structure. In the presence of SCC admixture, the microstructure displays a more dense arrangement of C–S–H. The active silica and alumina containing GCB reacted with Ca(OH)2 liberated from hydration of OPC phases producing additional CSH, which precipitated in some open pores, hence increases the compressive strength. Certainly, at later ages these pastes will outperform the control mixture of SCC. This type of high-strength, economical, self-consolidating, concrete has many applications in the construction industry, including precast concrete industry. The GCB increases the compressive strength of concretes at the ages of 28–1095 days, as evident from Figs. 5 and 6. The improvement of compressive strength is mostly due to the micro-filling ability and pozzolanic activity of GCB [43,44]. GCB fills the micro-pores within the cement particles. It readily reacts with
37.5% GCB
900
600
300
0 1
10
100
1000
Shear rate, s-1 Fig. 7. Effect of GCB powder on the variation of shear stress–shear rate.
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1500
100 OPC
37.5% GCB
0.0%
80
0.0%
1200
Shear stress, Pa
Shear stress, Pa
1.0% 1.5%
60 2.0%
40
0.5% 1.00
900
1.50 2.0%
600
300
20
0
0 1
10
100
1
1000
10
Fig. 8. Shear stress–shear rate of OPC cement pastes with different dosages of SCC admixture.
1000
Fig. 10. Shear stress–shear rate of 37.5% GCB–OPC cement pastes with different dosages of SCC admixture.
300
Reduction in shear stress, Pa
100 12.5% GCB
250
0.0% 0.5%
Shear stress, Pa
100
Shear rate, s-1
Shear rate, s-1
200
1.0% 1.5%
150
2.0%
100
80
60 1.0%
40
1.5% 2.0%
20
50
0
10
20
30
40
GCB, %
0 1
10
100
1000
Fig. 11. Effect of GCB powder on efficiency of SCC admixture.
Shear rate, s-1 Fig. 9. Shear stress–shear rate of 12.5% GCB–OPC cement pastes with different dosages of SCC admixture.
water as well as calcium hydroxide and produces additional C–S–H [43,44]. The additional C–S–H reduces the porosity of concrete by filling the capillary pores, and thus improves the microstructure of cement pastes in bulk paste matrix and transition zone leading to an increased in compressive strength. The strength of self-consolidating mortar and concrete systems depends on the maximum pore sizes and on the type and degree of pozzolanic activity of materials [45]. 3.2. Rheological properties Fig. 7 shows the effect of GCB on the obtained shear stresses. Increase of GCB content in cement pastes increase the shear stresses values. Fig. 8 represents the effect of self-compacting admixture on shear stresses of OPC cement pastes. It is clear that increase dosage of SCC admixture decreases the shear stresses. The decrease in shear stresses is due to chemical adsorption of SCC admixture on the cement grains. As the SCC admixture dosage increases, the surface increases and more dispersion is occurred leading to increase the paste workability. This is due to adsorption of superplasticizer on surface of the cement particles causing (i) creation of negative
charges on the cement particles, leading to an electrostatic repulsion with each other, (ii) lubricating effect on the mix, (iii) steric hindrance between the side branches of the superplasticizer, which increases the interparticles distance and gives the high fluidity. This effect also increases with the increase of polycarboxylate dosages [46]. Figs. 9 and 10 illustrate the rheological properties of cement pastes containing 12.5% and 37.5% GCB. Increase of GCB content increases the shear stresses values. It has been shown that the increase of SCC admixture dosages, the shear stresses values decreases. This behavior can be explained by superplasticizer adsorption and surface coverage by the adsorption of SCC admixture on the cement particles. An increase in polycarboxylate SCC admixture dosages leads to a higher surface coverage by polymers. At higher surface coverage the effective layer thickness increases and causes a reduction in the maximum attraction between the particles. Furthermore, the number of available nucleation sites decreases and the bridging distance between the particles increases. Less force is needed to disperse the particles, static yield stress and thixotropy become lower. The results illustrate the importance of understanding the interparticle interactions in concrete if rheological properties, workability and segregation resistances are to be controlled. Fig. 11 shows the effect of GCB on the efficiency of polycarboxylate SCC admixture (as reduction in shear stresses). The efficiency of polycarboxylate decreases as GCB content increases up to 12.5%,
M. Heikal et al. / Construction and Building Materials 38 (2013) 101–109
Fig. 12. SEM of cement paste containing 37.5% GCB filler cured at 7 days in the absence of SCC admixture.
Fig. 13. SEM of cement paste containing 37.5% GCB filler cured at 7 days in the presence of 1.5% SCC admixture.
whereas the efficiency increases with GCB content up to 37.5%. The decrease the reduction in shear stresses in presence of 12.5% GCB is due to filling effect; GCB fills some open pores between the cement particles. Increase of GCB up to 37.5% reduction in shear stresses increases, due to coating effect as well as steric hindrance of the long chain and high molecular weight of SCC admixture. 3.3. Scanning electron microscopy High resolution SEM gives useful information on the microstructure and phase composition of the hydration products. Figs. 12 and 13 show SEM micrographs of specimens containing OPC + 37.5% GCB hydrated at 7 days with and without SCC admixture. The hydration products appeared as nearly amorphous C–S–H covering the grains of anhydrous cement components; hexagonal crystals of Ca(OH)2 appeared in the structure (Fig. 12). The micrograph shows the flocculent and porous structures as well as wider pores are available for crystallization of the formed hydrates. Fig. 13 shows SEM micrograph of the hydrated products namely ill crystallized hydrated of calcium silicate, calcium aluminate and calcium sulphoaluminate (ettringite) hydrates, which deposited in some open space between the partially hydrated grains, that form a more dense structure is obtained. The pozzolanic reaction
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Fig. 14. SEM of cement paste containing 37.5% GCB filler cured at 28 days in the presence of 1.5% SCC admixture.
Fig. 15. SEM of cement paste containing 37.5% GCB filler cured at 366 days in the presence of 1.5% SCC admixture.
takes place between GCB and lime liberated during hydration of Portland cement phases forming additional hydration products (C–S–H) as well as fibrous calcium sulphoaluminate hydrates covered the surface of the cement specimens. The presence of admixtures does not seem to mainly affect the mechanical strength of the paste at 7 days of hydration with 1.5% SCC superplasticizer, and explained this development by the better dispersion of cement particles. The paste have smaller amounts of reaction products (C–S–H gel and CH crystals), their mechanical behavior appears to be more tightly is related to the pore structure and, very likely, to a better distribution of the different components. Figs. 14 and 15 show SEM micrograph of cement paste containing 37.5% GCB filler cured at 28 and 366 days in the presence of 1.5% SCC admixture. Fig. 14 represents micrograph of specimens containing 37.5 mass% of GCB in the presence of 1.5% SCC superplasticizer cured at 28 days. The presence of SCC superplasticizer, the microstructure displayed a more dense arrangement of microcrystalline C–S–H as the main hydration products with sheets of Ca(OH)2 as shown in the micrograph. SEM micrograph displays a large amount of CSH gel (Fig. 14). The gel is formed from the approaching the grains of GCB containing active silica and alumina with grains of Ca(OH)2 producing CSH and CAH hydrates, which fill some open pores to form compact structure, which improve the compressive strength. After 366 days (Fig. 15) of hydration more
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cement hydrates are deposited in pores space between the partially hydrated grains where a more dense structure is obtained and ill crystallized hydrates appeared as a clear binder between grains. The micrograph shows also longer rod like of CSH. GCB has a good pozzolanic activity in the presence of SCC admixture. The occurrence of CSH in large quantity is responsible for bridging cement particles, which producing a rigid closed compact structure. The micrograph picture reflects the high compressive strength obtained at later ages (28–1095 days as shown in Fig. 6). 4. Conclusions From the results presented in this paper, the following conclusions are offered: (1) The compressive strength of SCC decreased with GCB in the absence of SCC admixture. (2) Presence of SCC admixture, the compressive strength increases up to 28 days. (3) Increase of powder content of GCB up to 250 kg/m3, the compressive strength of concrete increases. (4) The compressive strength of OPC pastes increase with SCC admixture up to 1.5 mass%, whereas decreases with SCC admixture up to 2 mass% for 1095 days. (5) Pastes made with 12.5% and 37.5% GCB in the expanse of OPC pastes show higher strength values with SCC admixture at 28–1095 days. (6) Increase of GCB content increases the shear stresses values in cement pastes. (7) Increase of SCC admixture increases, shear stresses decrease, due to chemical adsorption of SCC admixture on the cement grains. (8) The efficiency of polycarboxylate SCC decreases as GCB content increases up to 12.5%, whereas the efficiency increases with GCB content up to 37.5%. (9) The presence of SCC superplasticizer, microstructure of GCB–OPC displayed a more dense arrangement of microcrystalline C–S–H as the main hydration products with sheets of Ca(OH)2 as shown in the micrograph, enhances the compressive strength.
References [1] Ozawa K, Maekawa K, Kunishima M, Okamura H. Performance of concrete based on the durability design of concrete structures. In: Proc. 2nd East asiapacific conf. on structural engineering and, construction; 1989. [2] Song HW, Byun KJ, Kim SH, Choi DH. Early-Age creep and shrinkage in selfcompacting concrete incorporating GGBFS. In: Proc. 2nd international RILEM symposium on self compacting concrete, Japan; 2001. p. 413–22. [3] Naik TR, Kumar R, Ramme BW, Canpolat F. Development of high-strength, economical self-consolidating concrete. Constr Build Mater 2012;30:463–9. [4] Bilodeau A, Sivasundaram V, Painter KE, Malhotra VM. Durability of concrete incorporating high volume of fly ash from source in US. ACI Mater J 1994;91(1):3–13. [5] Domone PL. Self-compacting concrete: an analysis of 11 years of case studies. Cem Concr Compos 2006;28(2):197–208. [6] Grdic´ Z, Despotovic´ I, Toplicic´ C´. Properties of self-compacting concrete with different types of additives. Architect Civil Eng 2008;6(2):173–7. [7] Yahia A, Tanimura M, Shimabukuro A, Shimoyama Y. Effect of rheological parameters on self compactability of concrete containing various mineral admixtures. In: Skarendahl A, Petersson O, editors. Proceedings of the 1st RILEM international symposium on self-compacting concrete, Stockholm, September, 1999. p. 523–35.. [8] Kurita M, Nomura T. Highly-flowable steel fiber-reinforced concrete containing fly ash. In: Malhotra VM, editors. Am Concr Inst SP 1998;178:159-175. [9] Kim JK, Han SH, Park YD, Noh JH, Park CL, Kwon YH, et al. Experimental research on the material properties of super flowing concrete. In: Bartos PJM, Marrs DL, Cleland DJ, editors. Production methods and workability of concrete. E&FN Spon; 1996. p. 271–84..
[10] Miura N, Takeda N, Chikamatsu R, Sogo S. Application of super workable concrete to reinforced concrete structures with difficult construction conditions. Proc ACI SP 1993;140:163–86. [11] Rizwan SA, Bier TA. Self-compacting mortars using various secondary raw materials. J ACI Mater 2009;106(1):25–32. [12] Rizwan SA, Bier TA. Early volume Changes of high-performance selfcompacting cementitious systems containing pozzolanic powders. In: Jensen OM, Pietro Lura, Konstantin Kovler, editors. Proceedings of international RILEM conference on ‘‘volume changes of hardening concrete: testing and mitigation’’, Lyngby, Denmark; 2006. p. 283–92. [13] De Schutter G. Durability of SCC-micro-structural considerations. Draft of ACI committee 2011;237:1–13 [revised chapter 9]. [14] Boukendakdji O, Kadri El-H, Kenai S. Effects of granulated blast furnace slag and superplasticizer type on the fresh properties and compressive strength of self-compacting concrete. Cem Concr Compos 2012;34(4):583–90. [15] Flatt RJ, Houst YFA. Simplified view on chemical effects perturbing the action of superplasticizers. Cem Concr Res 2001;31:1169–76. [16] Flatt RJ. Dispersion forces in cement suspensions. Cem Concr Res 2004;34:399–408. [17] Hanehara S, Yamada K. Rheology and early age properties of cement systems. Cem Concr Res 2008;21:175–95. [18] Sicker A, Huhn HJ, Mellwitz R, Helm M. The influence of admixtures on the rheological properties of mortars. LACER no. 2; 1997. [19] Collepardi M. Chemical admixtures today. In: Proceedings of second international symposium on concrete technology for sustainable February – development with emphasis on infrastructure, Hyderabad (India), 27 February–3 March, 2005; p. 527–41. [20] Assie S, Escadeillas G, Waller V. Estimates of self-compacting concrete ‘potential’ durability. Constr Build Mater 2007;21(10):1909–17. [21] Unal O, Topcu IB, Uygunoglu T. Use of marble dust in selfcompacting concrete. In: Proceedings of V symposium MERSEM0 2006 on marble and natural stone. Afyon (Turkey); 2006. p. 413–20. [22] Felekoglu B, Tosun K, Baradan B, Altun A, Uyulgan B. The effect of fly ash and limestone fillers on the viscosity and compressive strength of self-compacting repair mortars. Constr Build Mater 2006;36(9):1719–26. [23] Turkmen I. Influence of different curing conditions on the physical and mechanical properties of concretes with admixtures of silica fume and blast furnace slag. Mater Lett 2003;57(29):4560–9. [24] Sahmaran M, Christianto HA, Yaman IO. The effect of chemical admixtures and mineral additives on the properties of self-compacting mortars. Cem Concr Compos 2006;28(5):432–40. [25] Bosiljkov VB. SCC mixes with poorly graded aggregate and high volume of limestone filler. Cem Concr Res 2003;33(9):1279–86. [26] Corinaldesi V, Moriconi G. The role of industrial by-products in selfcompacting concrete. Constr Build Mater 2011;25(8):3181–6. [27] Babu KG, Kumar VSR. Efficiency of GGBS in concrete. Cem Concr Res 2000;30:1031–6. [28] Brooks J, Johari MAM, Mazloom M. Effect of admixtures on the setting times of high-strength concrete. Cem Concr Compos 2000;22:293–301. [29] Sonebi M. Medium strength self-compacting concrete containing fly ash: modelling using factorial experimental plans. Cem Concr Res 2004;34:1199–208. [30] Khayat KH, Bickley J, Lessard M. Performance of self-compacting concrete for casting basement and foundation walls. J ACI Mater 2000;97:374–80. [31] Uysal M, Yilmaz K. Effect of mineral admixtures on properties of selfcompacting concrete. Cem Concr Compos 2011;33(7):771–6. [32] ECP 203. 2007, The Egyptian code for design and construction of concrete structures – tests guide. Cairo (Egypt); 2007. [33] American Society for Testing and Materials American Society for Testing and Materials, ASTM Standards, Standard Test Method for Normal consistency of Hydraulic cement, American Society for Testing and Materials; 2008. p. C187– 83,195. [34] Heikal M, Aiad I, Helmy IM. Portland cement clinker, granulated slag and bypass cement dust composites. Cem Concr Res 2002;32:1809–12. [35] Kou S-C, Poon C-S. Properties of self-compacting concrete prepared with recycled glass aggregate. Cem Concr Compos 2009;31(2):107–13. [36] Bonavetti V, Donza H, Menández G, Cabrera O, Irassar EF. Limestone filler cement in low w/c concrete: a rational use of energy. Cem Concr Res 2003;33(6):865–71. [37] Lawrence P, Cyr M, Ringot E. Mineral admixtures in mortars effect of type, amount and fineness of fine constituents on compressive strength. Cem Concr Res 2005;35:1092–105. [38] Sari M, Prat E, Labastire JK. High strength self-compacting concrete –original solutions associating organic and inorganic admixtures. Cem Concr Res 1999;29(6):813–8. [39] Ghrici M, Kenai S, Meziane E. Mechanical and durability properties of cement mortar with Algerian natural pozzolana. J Mater Sci 2006;41:6965–72. [40] Uysal M, Yilmaz K. Effect of mineral admixtures on properties of selfcompacting concrete. Cem Concr Comp 2011;33(7):771–6. [41] Safiuddin MD, West JS, Soudki KA. Hardened properties of self-consolidating high performance concrete including rice husk ash. Cem Concr Compos 2010;32:708–17. [42] Uchikawa H, Sawaki D, Hanehara S. Influence of kind and added timing organic admixture on the composition, structure, and property of fresh cement paste. Cem Concr Res 1995;25:353–64.
M. Heikal et al. / Construction and Building Materials 38 (2013) 101–109 [43] De Sensale GR. Strength development of concrete with rice husk ash. Cem Concr Compos 2006;28(2):158–60. [44] Yu Q, Sawayama K, Sugita S, Shoya M, Isojima Y. The reaction between rice husk ash and Ca(OH)2 solution and the nature of its product. Cem Concr Res 1999;29(1):37–43.
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[45] Rizwan SA, Bier TA. Blends of limestone powder and fly-ash enhance the response of self-compacting mortars. Const Build Mater 2012;27:398–403. [46] Heikal M, Morsy MS, Aiad I. Effect of curing temperature on the electrical resistivity and rheological properties of superplastized blended cement pastes. L’industria Italiana del Cemento (iiC) 2004;802(10):772–85.
