Determination of tensile strain capacity of fresh concrete

Abstract

Measuring physical properties of fresh concrete is important to understand the behavior of the early phase of concrete. The measurement of tensile strain capacity of fresh concrete predicts the risk of cracking due to restrained shrinkage. Fresh concrete means the concrete before the hardening phase which is still in a semi liquid state. i.e. from right after mixing of concrete to 3 – 4 hours. Several research studies have been conducted but complex test methods have been developed to measure both stress and strain and the average strain was measured. The paper contains the procedure adopted to develop a simple test method to measure the local strain along a sample. After verifying the test method, influence of cement type for early age tensile strain capacity was studied. Ordinary Portland Cement, Fly ash blended and Portland Limestone Cement were used. Concrete was mixed as a large quantity and kept inside the mixer and agitated every 10 minutes before being taken out for testing. The method simulates the conditions where concrete is produced and kept inside a truck mixer for a while before placing. Results indicate that fly ash blended concrete has a higher tensile strain capacity than other cement types thus the mix is less vulnerable for early age cracking. Further tests should be done to determine the influence of cement type for tensile strain capacity of undisturbed concrete.