QUANTIFYING CEMENT CONTENT TO REGAIN THE COMPRESSIVE STRENGTH OF DELAY-CAST CONCRETE

Abstract

Retempering concrete is a common practice in the construction industry to restore its workability and compressive strength, despite the recommendation that concrete should be cast immediately after mixing with water. Casting delay significantly affects the concrete compressive strength and workability. This study aims to observe the effects of water and cement retempering on delayed casted concrete for up to 4 hours by measuring concrete compressive strength after 28 days of curing. Three variables; 1) retempering with water (RW), 2) 1^st retempering with a small amount of water and cement (RWC1), and 3) 2^nd retempering with a larger amount of water and cement (RWC2) were considered. Three concrete types having different coarse aggregates (crushed stone, uncrushed-round stone, and brick chips) were used. The results indicate that the compressive strength of crushed stone, single stone, and brick chip concrete was decreased after retempering with water (RW). Retempering with water and cement in different doses (RWC1 & RWC2) increased the compressive strength of the concrete. A regression model was used to quantify the needed cement (Kg/m³). Equations relating to casting delay and cement (Kg/m³) were also developed to gain the initial concrete compressive strength.