Abstract
Viscosity-enhancing agents (VEA) have been widely employed in high flowability cement-based materials, so as to ensure that no bleeding and segregation would occur. However, in most cases, interaction between VEA and superplasticizer would be unavoidable. In this study, the effect of polyacrylic acid (PAA), known as one of the most commonly used VEAs, on rheology performance of cement paste containing polycarboxylate superplasticizer (PCE), was studied. The initial fluidity was assessed with mini slump, and rheological behavior of cement paste was evaluated with rotor rheometer. Adsorption amount was examined with total organic carbon (TOC) analyzer, and the zeta potential was also tested. The interaction between PAA and PCE in the presence of calcium ion (Ca2+) was analyzed with conductivity, X-ray photoelectron spectroscope (XPS), and dynamic light scattering (DLS). The results illustrate that PAA can adsorb onto the surface of cement particles to plasticize cement paste, being similar to PCE. In the presence of Ca2+, PAA can be curled and crosslinked, as a result of the combination between carboxyl groups (COO−) and Ca2+, thereby affecting the adsorption performance and conformation behavior. It is interesting that negative impact of PAA on dispersion efficiency of PCE can be demonstrated; one reason is the reduced adsorption amount of PCE by PAA competitively adsorbing onto the cement surface, and another possible reason is the invalided PCE by adsorption of PAA. Additionally, molecular weight of PAA should be considered if being used as VEA in PCE system.
Highlights
No bleeding and segregation is mandatory in high fluidity cement-based materials, such as self-compacting concrete, self-leveling floor, and grout materials
The dispersion efficiency of Polycarboxylate superplasticizer (PCE) is closely related to the activity of long side chain (PEO, polyethylene oxide, which offers the steric hindrance as the main dispersion force) and the effective adsorption of PCE is the precondition for the effect of long side chain
Cement paste with Polyacrylic acid (PAA) (0.00%, 0.04%, 0.08%, 0.12%, 0.16%, 0.20% of cement) were prepared with water and cement ratio (W/C) of 0.5
Summary
No bleeding and segregation is mandatory in high fluidity cement-based materials, such as self-compacting concrete, self-leveling floor, and grout materials. This can be obtained with addition of viscosity-enhancing agent (VEA) and superplasticizer [1,2,3]. The intercalation of PCE can be enhanced by STPP to further invalid the PEO, and in this case, the dispersion efficiency of PCE would be declined immediately [15]. These conclusions would be expected to offer useful experience for the use of viscosity-enhancing agent in concrete engineering
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