Physico-mechanical properties of composite cement pastes containing silica fume and fly ash

AbstractThis works aims to study the effect of partial substitution of ordinary Portland cement (OPC) by silica fume (SF) and fly ash (FA) on the physico-mechanical properties of the hardened OPC–FA–SF composite cement pastes. The OPC was partially replaced by 20% and 30% fly ash along with 5% and 10% silica fume. The phase composition of the hydration products was investigated using XRD and DTA techniques. It was found that, the increase of FA content in OPC–FA–SF composite cement decreases the water consistency values and increases the setting times. On the other hand, the increase of SF content leads to increase the water of consistency and decrease the setting times. The partial substitution of OPC by FA and SF leads to higher porosity values with a consequent decrease in the compressive strength values especially during the early ages of hydration. At the later ages of hydration, however, the OPC–FA–SF cement pastes possess total porosity and compressive strength values close to those of the neat OPC paste. The lower of free lime contents were obtained for OPC–FA–SF composite cement pastes with the formation of further additional amounts of CSH as a result of the pozzolanic reaction. The results showed also that, the physico-mechanical properties of composite cement paste [OPC (65%)–FA (30%)–SF (5%)] were improved at later ages

Kinetics and physico-chemical properties of alkali activated blast-furnace slag/basalt pastes

AbstractGranulated blast-furnace slag (GBFS) is a by-product of the metallurgical industry and consists mainly of lime and calcium–magnesium aluminosilicates that defined as the glassy granular material formed by rapid cooling of molten slag with excess water resulting in an amorphous structure. Alkali-activated slag (AAS) binders have taken a great interest from researchers due to its manufacturing process which has important benefits from the point of view of the lower energy requirements and lower emission of greenhouse gases with respect to the manufacturing of Portland cement. In this study, GBFS was replaced by 20, 40 and 60wt.% of basalt activated by 6wt.% of alkali mixture composed of 1:1 sodium hydroxide (SH) and liquid sodium silicate (LSS) mixed with sea water and cured in 100% relative humidity up to 90days. The physic-chemical parameters were studied by determination of setting time, combined water content, bulk density and compressive strength. As the amount of basalt increases the setting time as well as compressive strength decreases while the bulk density increases. The compressive strength values of dried pastes are greater than those of saturated pastes. The hydrated products are identified by TGA/DTG analysis, IR spectroscopy and scanning electron microscopy (SEM)

Preparation of β-dicalcium silicate (β-C2S) and calcium sulfoaluminate (C4A3S¯) phases using non-traditional nano-materials

This paper describes the synthesis of some nano-compounds such as SiO2, Al(OH)3 and Ca(NO3)2 which can be used in the preparation of nano β-C2S as well as nano C4A3S¯. The preparation of β-C2S from nano-SiO2 and Ca (NO3)2 in comparison with traditional materials such as Ca(CH3COO)2, CaCO3 and silica quartz fired at different temperature has been studied. Also, C4A3S¯, can be prepared from nano-materials such as Ca(NO3)2 and Al(OH)3 with pure gypsum in comparison with Ca(CH3COO)2, CaCO3 and calcined Al2O3. The rate of formation of β-C2S and C4A3S¯, can be also studied after firing with chemical and XRD methods. These phases were obtained by crystallization processing at different temperatures. The formation of these phases was monitored by measuring the free lime and insoluble residue contents. The results showed that the extent of formation was found to be much higher with nano-materials as compared to those prepared in a conventional manner. The prepared belite phase from nano-silica and calcium nitrate reduces the temperature synthesis to 1150 °C. Also the preparation of C4A3S¯ from nano Al(OH)3 and Ca(NO3)2 and pure gypsum fired at 1290 °C, was the perfect composition to produced a well formed calcium sulfoaluminate phase in comparison with traditional materials