Abstract
The effect of individual and combined addition of both nanosilica (NS) and polycarboxylate ether plasticizer (PCE) admixtures on cements pastes was studied. The sole incorporation of NS increased the water demand, as proved by the mini-spread flow test. An interaction between NS and hydrated cement particles was observed in fresh mixtures by means of particle size distribution studies, zeta potential measurements and optical microscopy, giving rise to agglomerates. On the other hand, the addition of PCE to a cement paste increased the flowability and accelerated the setting process. PCE was shown to act in cement media as a deflocculating agent, reducing the particle size of the agglomerates through a steric hindrance mechanism. Mechanical strengths were improved in the presence of either NS or PCE, the optimum being attained in the combined presence of both admixtures that involved relevant microstructural modifications, as proved by pore size distributions and SEM observations. The results indicate also the effectiveness of NS and polycarboxylate superplasticizer in producing high packing density and in accelerating the pozzolanic activity to produce more C-S-H gel by consuming calcium hydroxide Ca(OH)2 in order to improve the mechanical properties of cement pastes. Key words: Cement pastes, polycarboxylate plasticizer, nanosilica, optical microscopy, rheological and electrokinetical properties.
Highlights
During the mixing, the cement particles are dispersed and suspended in water
Rheological tests are performed for cement pastes based on two types of cement C2 and C3 at different dosages of adjuvant to study the behavior of cement pastes and determining the saturation point for each type of cement
For adjuvanted cement grout, we find that: The adjuvant Aeternum-1 significantly affects the viscosity of the cement paste, and its content increases more, the viscosity of the paste decreases more
Summary
The cement particles are dispersed and suspended in water. In the presence of a superplasticizer, the cementitious paste becomes more stable and the shortage of water which affects the maniability of cementitious pastes in time will be resolved in the presence of a superplasticizer. Many research studies have shown that several factors affecting the rheological stability of the cement pastes namely; the concentration of solids, the cement characteristics and the nature and dosage of the superplasticizer used. The essential purpose of the use of a superplasticizer is to disperse the cement grains.
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