STUDY OF SELF LEVELLING PASTE SYSTEMS USING BLENDS OF CALCIUM ALUMINATE CEMENT AND PORTLAND CEMENT AT VARIABLE MIXING WATER TEMPERATURE

Abstract

Rapid Hardening Self levelling Cementitious Systems are known for their applications in emergency repair work on runways, bridges and tunnel linings. They also provide excellent solutions for Self levelling underlayments. The aim of our research was to investigate effect of mixing water temperature on multi-binder systems. CAC was used to help accelerate the setting times of OPC. However, the drawback of using CAC is its strength degradation over time, a process known as Conversion. Our objective was to study this Conversion process under variable mixing water temperature. The water temperatures tested were 5◦C, 23◦C and 35◦C. Binary formulations were studied with varying percentage of CAC as a replacement to OPC. A ternary blend of CAC-OPC-Fly Ash was also studied under variable water temperature to study the behavior of Fly-Ash in binary Self Levelling Paste (SLP) Systems. Tests conducted for SLP formulations were water demand, setting times, compressive strengths, calorimetry and shrinkage. Charts were plotted against each test and the effect of mixing water temperature was observed. Other tests performed were BET surface area, Particle Size Analysis (PSD), XRD and XRF. It was found that: Binary SLPS of CAC-OPC cause faster setting in comparison with their parent formulations (CAC, OPC). This leads to higher water demands and plasticizer dosage. However, it was seen that for Cold Mixing Water, the water demands and SP demands decreased with increasing CAC replacement in OPC. At higher mixing water temperature, the trend reverses: Water demands and SP demands increase with increasing CAC replacement in OPC. Setting Times increased with increasing CAC replacement at cold mixing water temperatures and decreased at elevated temperatures. The replacement of OPC with Fly Ash retarded setting times at Cold water temperatures but this effect was not observed at elevated temperature. Compressive strengths were also plotted for 1 day, 7 day and 28 days of water curing against varying mixing water temperatures. Contrary to what literature suggested, the final 28 day strength of binary formulations was higher than that of 100% OPC and 100%CAC. Also, the conversion phenomenon was not observed at colder mixing water temperature but at elevated temperature (35◦C), 28 days compressive strength of CAC decreased compared to 7 day strength. Calorimetry was also performed for SLP formulations and temperature graphs were plotted for 1 day Hydration. It was seen that CAC gave the highest temperature peak followed by OPC, and their binary blends. XRD tests confirmed presence of di-calcium Aluminum Hydrates in pure CAC samples hydrated at 56 days which proved that conversion phenomenon requires higher mixing water temperatures above 35◦C as well as more curing time. Presence of fast setting Ettringite was also confirmed in binary CAC-OPC blends In short it can be concluded that elevated mixing water temperature greatly reduces setting times for binary blends of CAC-OPC but increases water demand and SP demand and reduces workability. Also strength is greatly reduced at higher temperatures owing to Conversion phenomenon as well as increased water demand which creates more voids.