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)

Application of microbial biocementation to improve the physico-mechanical properties of cement mortar

AbstractCalcite is one of the most common and wide spread mineral on Earth constituting 4wt% of the Earth’s crust. It is naturally found in extensive sedimentary rock masses, as lime stone marble and calcareous sandstone in marine, fresh water and terrestrial environments. Calcium carbonate is one of the most well known mineral that bacteria deposit by the phenomenon called biocementation or microbiologically induced calcite precipitation (MICP). Such deposits have recently emerged as promising binders for protecting and consolidating various building materials. Microbially enhanced calcite precipitation on concrete or mortar has become an important area of research regarding construction materials. This study describes a method of strength and water absorption improvement of cement–sand mortar by the microbiologically induced calcium carbonate precipitation. A moderately alkalophilic aerobic Sporosarcina pasteurii was incorporated at different cell concentrations with the mixing water. The study showed that a 33% increase in 28days compressive strength of cement mortar was achieved with the addition of about one optical density (1OD) of bacterial cells with mixing water. The strength and water absorption improvement are due to the growth of calcite crystals within the pores of the cement–sand matrix as indicated from the microstructure obtained from scanning electron microscopy (SEM) examination

A novel method to produce dry geopolymer cement powder

Geopolymer cement is the result of reaction of two materials containing aluminosilicate and concentrated alkaline solution to produce an inorganic polymer binder. The alkali solutions are corrosive and often viscous solutions which are not user friendly, and would be difficult to use for bulk production. This work aims to produce one-mix geopolymer mixed water that could be an alternative to Portland cement by blending with dry activator. Sodium hydroxide (SH) was dissolved in water and added to calcium carbonate (CC) then dried at 80 °C for 8 h followed by pulverization to a fixed particle size to produce the dry activator consisting of calcium hydroxide (CH), sodium carbonate (SC) and pirssonite (P). This increases their commercial availability. The dry activator was blended with granulated blast-furnace slag (GBFS) to produce geopolymer cement powder and by addition of water; the geopolymerization process is started. The effect of W/C and SH/CC ratio on the physico-mechanical properties of slag pastes was studied. The results showed that the optimum percent of activator and CC content is 4% SH and 5% CC, by the weight of slag, which give the highest physico-mechanical properties of GBFS. The characterization of the activated slag pastes was carried out using TGA, DTG, IR spectroscopy and SEM techniques

Utilization of microbial induced calcite precipitation for sand consolidation and mortar crack remediation

The microbes can hydrolyze urea by urease enzyme to produce ammonium as well as carbonate ions and in the presence of calcium ions which can precipitate calcium carbonate; this process is called “biocalcification” or microbial induced calcite precipitation (MICP).This technology is environmentally friendly not only because it gives strength to sand body, but also it allows water to penetrate to sand body, which is unlike silicate cement that will destroy the ecosystem of the earth. Calcium carbonate precipitated by bacteria acts as a binding material to sand particles, so incompact sand will be consolidated. Calcium chloride, calcium acetate and calcium nitrate (1 M) as calcium sources were tested for their ability to consolidate sand by mixing with urea (1 M) and bacteria cells (one optical density, 1 OD). The key point of this study aimed to choose the suitable calcium source which produces higher compressive strength and lower water absorption. The results showed that the degree of crystallinity and amount of precipitated calcium carbonate, as well as the consequent increase in strength of consolidated sand, in case of calcium chloride medium are higher than those precipitated in case of calcium acetate as well as calcium nitrate media. In addition, consolidated sand by calcium chloride was also used for cement mortar crack remediation

Recycling of concrete waste to produce ready-mix alkali activated cement

Ceramics International Volume 44, Issue 6, 15 April 2018, Pages 7300-7304The goal of this study is to produce an environmentally, and user friendly ready-mix alkali activated cement (RM-AAC) by thermal activation of concrete waste (CW) in the presence of sodium hydroxide (NaOH). Two major compositional factors, which play an important role in the performance of RM-AAC, i.e. temperature and NaOH percentage, were investigated. The CW showed high stability under thermal treatment up to 1200 °C; meanwhile it can be converted to distorted structure with high amorphicity in the presence of appropriate NaOH content. RM-AAC powder can react with water, forming hardened material with an acceptable compressive strength. Due to the white color of RM-AAC powder, it can be beneficially used in prestige construction projects and decorative works