Using viscosity-modifying admixture to increase the cohesion of low-cement concrete mixture

Low-cement concrete (LCC) is made by considering the particle packing of the constituent material. The minimal content of cement paste is achieved by optimizing the coarse and fine aggregate particle size gradation to reduce the void volume (Vv) between the aggregate particles. Theoretically, the minimum cement paste can be calculated as the cementitious paste volume (Vp) filling the entire void volume (Vp/Vv = 100%). Practically, low fine or powder material content would reduce concrete mixture cohesion and cause bleeding and segregation. Viscosity-modifying admixture (VMA) can be added as an alternative to adding more cement powder or supplementary cementitious materials to improve the cohesion and stability of the LCC matrix. This study investigated the role of VMA addition in increasing stability in low water to cement ratio (w/c) mortar with an excessive dosage of superplasticizer and in high w/c mortar designed with low cement content. The results showed that adding VMA reduced bleeding and increased cohesion in the fresh mixture, and also increased the compressive strength of the hardened mortar. Although the addition of VMA cannot increase the workability of LCC, it had a beneficial effect when added to an LCC mixture as the 28-day compressive strength of the concrete with w/c of 0.5 was increased from 18.68 MPa to 22.93 MPa by adding 0.4% VMA by mass of cement. (paper)