The influence of the ageing of calcium aluminate cement on the properties of mortar

Abstract

This paper presents an on-going study of the influence of the ageing of calcium aluminate cement (CAC) and its mixtures with additives on the properties of fresh and hardened mortar without any deflocculants. DTA, TG, XRD, and SEM methods for hardening products and structure analysis and as well methods for evaluation technical characteristics of mortar, such as the flowability, compressive strength, density, and ultrasonic wave propagation velocity, were used in the work. The results revealed that the ageing of the raw materials in a climatic chamber at 95% relative humidity (RH) and 20 ± 1 °C for 7 days caused a decrease in the flowability of fresh mortar. This characteristic was also influenced by the properties of the additives. The mortar prepared from 14-days-aged raw materials was not flowable. The overall weight loss upon heating and the XRD data indicated a significant increase in the hydration products formed during mortar hardening when the ageing time of the raw materials was extended from 7 to 14 days compared to the amount of hydration products in the hardened mortar prepared from 7-days-aged raw materials. This increase is probably due to the peeling of the carbonated hydration products of cement particles, formed during ageing for 7 days, from the surface when the ageing time is prolonged beyond 7 days, leading to an increased hydration of the cement particles. The ageing of the raw materials has a negative effect on the compressive strength and density of hardened mortar. The formation of hydration products during mortar hardening and the compressive strength and density are affected by the properties of the additives.