The effect of different cement and calcium sulphate samples on the physical and chemical properties of self leveling screeds

In the rapidly growing construction sector in Turkey, the importance given to building efficiency is increasing. Self-leveling screeds (SLM) and concretes were developed for this purpose. In this study, single, double and triple binder systems consisting of Portland cement (OPC), calcium aluminate cement (CAC) and calcium sulphate source (CŚ), which are used in SLM formulations, are taken referance. The effects of different compositions of these systems on the physical and chemical structure of the mortar were investigated. Set starting and ending times of fresh mortars at constant water/binder ratio were tested. Bending and compressive strengths, shrinkage/expansion ratios at dfferent curing times were measured. At the same time, hydration mechanisms of mortar systems were tried to be understood from obtained by X-ray flourescence spectrophotometer (XRF) and Scanning Electron Microscope (SEM). According to results obtained, it was determined that R2 sample containing %80 OPC and %20 CAC (R2) at a water/binder ratio of 0,4 accelerated the setting start times in hydration process from 240 minute to 15 minute in hydration compared to R1 specimen containing %100 Portland Cement. Despite of this effect, it was observed that the compressive strength of the R1 sample decreased from 18,98 MPa to 13,43 MPa after 1 day. In order to minimize this negative effect caused by rapid etrengite formation, it was determined that the low ratio of anhydrite (A1), one of the CŚ sources added, had the best effect with 16,12 MPa in early strength. D1 sample containing low amount of dihydrate gave the best result after 28 days. The compressive strength of specimen of D1 was 44,28 MPa, while the compressive strength of specimen of R1 containing % OPC was measured 48,82 MPa. The hemihydrate had no effect on the shortening of the setting time caused by the CAC cement. When all trials were compared, the highest shrinkage/expansion value of %2,4 was determined in D2 sample in which dihydrate is used at high ratio.