Heat flow and strength properties of perspective hydraulic binder material

Abstract

In this work, the results of preparing a novel hydraulic binder material on a-C 2 SH basis using both chemically pure and natural raw materials are presented, as well as hydration and strength properties of such binders are described. a-C 2 SH was hydrothermally synthesized at 200°C for 8 h from reagents (CaO, SiO 2 ÁH 2 O) and for 4 h from natural rocks (decalcinated chalk marl, opoka). DSC and XRD analysis showed that remaining portlandite and part of a-C 2 SH decompose during 5 min of intensive tribochemical activation of the synthesis products and quartz mixture. Unfortunately, according to TG data, water released from these compounds remains in the sample. Applying different types of mills as well as the adding water adsorbents (CaO, CaCl 2 and BaO) has no effect on the hydraulic activity of the binder: The results of microcalorimetric analysis indicate that heat flow values of the main hydration reactions decreased in all cases. Most suitable way of removing water from the samples is lowtemperature thermal treatment at 450°C. Milled a-C 2 SHquartz mixture exhibited good binding properties after burning mixtures at this temperature. The mortar with the highest compressive and bending strength values (20.43 and 5.17 MPa after 28 days of hydration) was obtained using mixture which consisted of 25 % (by mass) synthesis product (obtained from hydrothermal synthesis of opoka and chalk marl), 25 % together with a-C 2 SH-milled quartz sand (during the tribochemical activation) and 50 % standard sand.

Part 1: A study on the properties of synthetic hydroxyledgrewite

“…It is worth mentioning that obtained results differs from literature, there the hydrothermal synthesis of dibasic calcium silicates hydrates were examined in detail. In these works, afwillite, hillebrandite, α‐C 2 SH, and other C‐S‐H where synthesized, however hydroxyledgrewite was not obtained. Presumably, the differences between obtained results and those of literature arose due to nature and reactivity of used raw materials.…”

“…It is known that in order to achieve hydraulic activity of dibasic calcium silicates hydrates, they must be activated (for example, by milling) with another inert component containing SiO 2 such as quartz and, subsequently, thermally treated . In this case, hydrogen bonds are destroyed and reactive fragments are deposited in disordered state on the silicate surfaces.…”

“…The further increment of calcination temperature (900°C) gives negatively effect on the amount of released heat (Figure ). According to literature, the amount of total cumulative heat, after activation of the most used dibasic calcium silicate hydrate—α‐C 2 SH, is equal to 40‐230 J/g. For this reason it is probably that hydroxyledgrewite after activation can be used as alternative cementitious material.…”

Pilot Study of Mechanical Waves Passing through Fine-Grained Cement Composite during the Early Hydration Process

“…Mechanical waves passing through cement composites during their hydration can reveal individual stages of hydration of the composite. Cement is a hydraulic binder which sets and hardens as a result of hydration reactions after mixing cement with water and after hardening, maintains its strength and stability, both in air and in water [4,5,6]. Put simply, the internal structure changes from suspension through elastic phase to hardened mass during the hydration process.…”