Full Length Article Effect of calcium chloride on the hydration characteristics of ground clay bricks cement pastes Essam A. Kishar, Doaa A. Ahmed*, Maha R. Mohammed, Rehab Noury Chemistry Department, Faculty of Girls, Ain Shams University, Cairo, Egypt article info Article history: Received 15 July 2012 Accepted 20 December 2012 Available online 13 September 2013 Keywords: Blended Portland cement Calcium chloride Ground clay bricks Cement hydration abstract Effect of CaCl 2 on the hydration characteristics of the different cement pastes using ordi- nary Portland cement (OPC) and blended Portland cement with ground clay bricks (GCB) was studied. Various mixes were prepared using a water/solid ratio (W/S) of 0.25 (by weight). Three percentages of CaCl 2 (0.25, 0.5 and 0.75%) are used; the CaCl 2 used was dissolved in the mixing water. The hydration characteristics were tested via the determi- nation of the combined water content, phase composition, compressive strength, total porosity (P%) and X-ray diffraction analysis (XRD) at different time intervals up to 180 days. The results showed that calcium chloride accelerates cement hydration in all systems studied. Ten % GCB in the presence of 0.50% CaCl 2 is the optimum ratio which has the higher compressive strength. Copyright 2013, Beni-Suef University. Production and hosting by Elsevier B.V. All rights reserved. 1. Introduction Super-plasticizers are admixtures, which are added to con- crete mixture in very small dosages. Their addition results in significant increase of the workability of the mixture, in reduction of water/cement ratio or even of cement quantity. Their performance depends on the type of the super- plasticizer, the composition of the concrete mixture, the time of addition and the temperature conditions during mix- ing and concreting (Papayianni et al., 2005). The influence of the presence of concrete admixtures on the hydration reaction of cement pastes was studied. Two admixtures (1) an accelerator and (2) a retarder, have been added to the cement pastes at different ages. The presence of such admixtures affects the physicochemical properties of the products. The addition of the accelerator the rate of hydration reaction whereas the retarder delays the reaction rate; the intensity of X-ray increases diffraction peaks characterizing the formed phases during the hydration reaction is generally increased in the presence of the accelerator and reduced with the retarder (Ismail and El-Hemaly, 1991). Calcium chloride is the most widely used because of its ready availability and low cost. CaCl 2 has long been known to accelerate both the setting and hardening of Portland cement concrete, the effect of * Corresponding author. E-mail address: [email protected](D.A. Ahmed). Peer review under the responsibility of Beni-Suef University Production and hosting by Elsevier Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/bjbas beni-suef university journal of basic and applied sciences 2 (2013) 20 e30 2314-8535/$ e see front matter Copyright 2013, Beni-Suef University. Production and hosting by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.bjbas.2013.09.003
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Effect of calcium chloride on the hydration ... · cement paste. It is concluded that the addition of calcium chloride can partially inhibit the cracking caused by drying and sorption
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b e n i - s u e f un i v e r s i t y j o u rn a l o f b a s i c a n d a p p l i e d s c i e n c e s 2 ( 2 0 1 3 ) 2 0e3 0
Available online at w
ScienceDirect
journal homepage: www.elsevier .com/locate/bjbas
Full Length Article
Effect of calcium chloride on the hydrationcharacteristics of ground clay bricks cement pastes
Essam A. Kishar, Doaa A. Ahmed*, Maha R. Mohammed, Rehab Noury
Chemistry Department, Faculty of Girls, Ain Shams University, Cairo, Egypt
b e n i - s u e f un i v e r s i t y j o u rn a l o f b a s i c a n d a p p l i e d s c i e n c e s 2 ( 2 0 1 3 ) 2 0e3 030
peaks of CH as one of the more crystallized hydration prod-
ucts, gradually increaseswith increasing hydration age, due to
the progress of hydration of Portland cement constituents. On
the other hand, the intensity of the peaks characteristic of the
reactants such as alite and belite phases decreases with
increasing the hydration age. It can be noticed that the in-
tensity of CH peaks in presence of CaCl2 is higher than those in
absence of the salt at all hydration ages for all mixes. This
indicates that CaCl2 accelerates the hydration of Portland
cement components.
3.5. Thermal analysis
Figs. 7 and 8 show the DTA curves of the control mixes (MI,
MII) in absence and presence of 0.25 and 0.75% CaCl2 (w/w)
hydrated for 180 days. The endothermic peaks in the DTA
curves at 50e120 �C can be attributed to the evaporation of the
physically and chemically combinedwater in CSH (Dweck and
Buchler, 2000; Dweck et al., 2003). While as, the endothermic
peaks at about 450 �C may be due to the decomposition of
calcium hydroxide (CH). Obviously, the endothermic peaks of
the decomposition of CSH and CH in presence of CaCl2 are
higher than those of the control mixes. This indicates that the
presence of CaCl2 causes acceleration of the hydration reac-
tion of Portland cement (formation of CH). The intensity
endothermic peak located at 450 �C increases in with
increasing the amount of CaCl2. Such observation supports
the results obtained from the X-ray diffraction analysis.
4. Conclusions
The main points that could be derived from this study are
summarized in the following:
1 The combined water contents increase with calcium
chloride at all the hydration ages. This may be attributed
to the acceleration effect of CaCl2.
2 All the investigated cement pastes containing CaCl2showed higher values of compressive strength than those
of the control samples.
3 The porosity of cement pastes containing CaCl2 is lower
than those in the control samples (without CaCl2). This
may be due to the formation of more hydration products
which fill the pores of the hardened cement pastes.
4 The results of X-ray diffraction analysis indicate that the
degree of hydration of samples with calcium chloride is
higher than that of samples without calcium chloride,
which prove the acceleration effect of CaCl2.
5 The results of thermal analysis of some selected samples
indicate that the degree of hydration of samples con-
taining calcium chloride is more than that of the samples
without calcium chloride. This indicates that the presence
of CaCl2 favors the formation of CSH with high water
content.
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