Early Age Stress Development, Relaxation, and Cracking in Restrained Low W/B Ultrafine Fly Ash Mortars

Abstract

This paper describes an experimental study that investigated the influence of ultrafine fly ash (UFFA), a relatively new pozzolanic admixture, on the early age stress development, stress relaxation, and cracking in restrained low water-tobinder ratio (w/b) mortars due to shrinkage. The restrained ring test was used to assess the early age residual stress development in mortar ring specimens. In addition, free shrinkage strain, elastic modulus, and splitting tensile strength measurements were performed to assess the stress relaxation (creep effect) and cracking potential. It was found that the restrained mortar mixtures containing the typical fly ash (FA) (ASTM Type-F) or the ultrafine fly ash demonstrated lower levels of residual tensile stress than the control mixture. Also, both typical fly ash mortar and ultrafine fly ash mortars demonstrated a reduction in free shrinkage. In addition, an increase in the age of cracking and a decrease in stress relaxation (creep effect) were observed in the restrained mortar ring specimens containing FA or UFFA. However, at equal replacement of cement with either FA or UFFA, the delay in the age of cracking and the reduction in stress relaxation were higher for the UFFA modified mortar.

Material and Structural Performance Evaluations of Hwangtoh Admixtures and Recycled PET Fiber-Added Eco-Friendly Concrete for CO2 Emission Reduction

“…Numerous works on concrete admixtures show that the major obstacle in using admixtures in ordinary Portland cement (OPC) concrete for actual construction is the 30% maximum limit in the cement substitution ratio. According to most studies, when the maximum substitution percentage is violated, reductions in properties of strength, crack resistance, and overall material performance are observed [14,17,18,19,20]. Therefore, a solution to the problem of how to increase the admixture substitution ratio in a concrete mix without decreasing the final performance of the material is needed in order to develop useable eco-friendly concrete.…”

Assessment of behaviour and cracking susceptibility of cementitious systems under restrained conditions through ring tests: A critical review

“…In this article, a state-of-the-art review of the widely adopted ring test method for the evaluation of the risk of cracking of cementitious materials under restrained shrinkage has been presented. Based on the review of the literature, statistical analysis and discussions, the following conclusive observations can be made: [41]  It appears that the standardisation of the ring test as a method to examine cracking sensitivity of cement-based materials promoted significantly its use. Thanks to standardisation, in a considerable amount of studies over the last fifteen years, research on restrained shrinkage has been conducted using such experimental method.…”

Environmental load for design of airport concrete pavements

“…Park et al (2009) measured the strains of steel and concrete at various positions of confined and unconfined ring specimens and an unconfined square prism specimen. The strains were used as the input variables in elastic stress and residual stress prediction models (Hossain et al, 2008) to calculate the stress relaxation by subtracting the residual stress from the elastic stress. The rate of stress relaxation in Equation 7 is defined as the variation of the ratio of relaxed stress to elastic stress according to concrete age.…”