Water transport and shrinkage in concrete made with ground recycled concrete-additioned cement and mixed recycled aggregate

This article reports on analytical research into water transport in concrete with 10%-25% ground recycled concrete (GRC) as partial Portland cement replacement and 0% or 50% mixed recycled aggregate (MRA). It included analyses of durability indicators associated with water transport: effective (or open) porosity, penetration depth of water under pressure, permeability coefficient, capillary water absorption and electrical resistivity. Shrinkage was also monitored in all concrete samples. The findings showed that replacing up to 25% OPC with GRC induced a linear rise in effective porosity of up 11.4% in concrete with 100% NA and 33% in mixes with 50% MRA, relative to conventional concrete. The outcome, a tightly interconnected pore structure, lowered electrical resistivity by 14% in NA and 23% in MRA GRC-additioned cement concrete. That pore structure was nonetheless sufficiently impermeable to ensure suitable concrete durability, with penetration depth of water under pressure below 30 mm, a permeability coefficient below 10(-12) m/s and sorptivity below 1 mm/h(0.5). The three-way ANOVA conducted revealed that adding GRC was the factor with the greatest impact on penetration depth of pressurised water, permeability coefficient and sorptivity. Curing time was the most statistically significant factor for electrical resistivity and shrinkage in both mix families (NA and GRC), inasmuch as it determined the degree of hydration of the anhydrous phase in GRC and in the residual mortar bound to MRA components. Further to the present findings, the use of GRC at a replacement ratio of up to 10% does not lower recycled material concrete's durability relative to the mixes made with ordinary Portland cement.

Automated summary

The research found that partial replacement of Portland cement and aggregate in concrete can increase porosity and reduce electrical resistivity, without compromising durability. The addition of GRC had the greatest impact on penetration depth of pressurized water, permeability coefficient, and sorptivity, while curing time had the most significant effect on electrical resistivity and shrinkage.