Properties Of Alkali-activated Concrete Research Articles

Influence of ultra-fine steatite powder on the properties of alkali-activated concrete

Alkali-activated binders are emerging sustainable binders in the construction sector due to their higher strength and superior resistance against aggressive environments than those of cement concrete. Steatite powder is obtained as a by-product of soapstone processing and disposed of as waste in large quantities. Studies on the reuse of steatite powder in alkali-activated concrete are few. Hence, the current research focuses on the influence of ultra-fine steatite powder on the mechanical as well as durability properties of slag- and fly-ash-based alkali-activated concrete. Six replacement levels (10, 20, 30, 40, 50 and 60%) of slag and fly ash with steatite powder were adopted and activated using a sodium-based activator. Heat curing and ambient curing were performed for fly ash–steatite concrete and slag–steatite concrete, respectively. From the test results, 30% steatite powder is the optimum for slag- and fly-ash-based alkali-activated concretes. Less water absorption and higher resistance against acid exposure are observed for steatite-based alkali-activated concrete specimens.

Optimization of alkali-activated concrete based on the characteristics of binder systems

The characteristics of binder systems played vital roles on the properties of alkali-activated concretes (AACs), from strength development to long-term durability. Here, the sum of 102 binder systems with three levels of alkalinity of 5%, 6%, and 7% and three levels of blast furnace slag to fly ash mass ratio of 50:50, 60:40, and 70:30 activated by diverse compositions of activators (single sodium hydroxide, sodium silicate, and sodium carbonates or combination) were investigated. Based on that, a series of compositions-properties contours/maps considering the hardening strength, shrinkage behavior, and mechanical characters of these binder systems have been established. After that, a modified overall-calculation method was applied for the mix design of concrete. The AACs performance including basic mechanical behaviors in compression, flexure, and tensile load and volume stability (including drying shrinkage and alkali-aggregates reaction) were checked. It’s suggested that the performances of AACs were in a broad range depended on the binder systems. Thus, the selection of binder systems was in the most important position in designing concrete even other aspects, for example, aggregates type would also affect performances like mechanical and shrinkage of AACs. However, the complexity of alkali-activated binder systems make it difficult to establish the quantitative relationships between compositions and performances of AACs. Therefore, the compositions-properties contours/maps established here would deep the understanding for roles of constituents on the performances of AACs and guide the optimization of AACs in practice.

Sustainable utilization of ultrafine rice husk ash in alkali activated concrete: Characterization and performance evaluation

This paper investigates the novel effect of ultrafine rice husk ash (URHA) on the properties of alkali-activated concrete. Rice husk ash was obtained as waste from biomass energy production and further processed to obtain URHA. The URHA was first characterized using various techniques to understand its morphology, structure and chemical composition. The URHA was then used to replace fly ash in alkali-activated fly ash/slag concrete up to 10%, and the effects on the performance were evaluated. The optimum dosage of URHA was assessed based on the compressive strength and the resistance to chemical attacks was carried out on the control mixture and that incorporating the optimum URHA. Microstructural properties of some of the control mixture and that incorporating the optimum URHA content was also investigated. Results from this study showed that the use of URHA as a 5% replacement of the FA is optimum that ensured high performance.

Influence of nano-SiO2 on the strength and microstructure of natural pozzolan based alkali activated concrete

Development of alkali-activated binder (AAB) is fast becoming a viable alternative to ordinary portland cement (OPC). However, key engineering properties of such a binder depend strongly on the chemical composition and fineness of the source materials in addition to the concentration of alkaline activators. In order to improve the reaction kinetics and subsequently, the mechanical strength of alkali activated concrete (AAC), nano-SiO2 was proposed as a partial replacement to natural pozzolan (NP) in this study. As the composition of alkaline activators also plays a vital role on the properties of AAC, trial mixtures were prepared with varying sodium silicate to sodium hydroxide (SS/SH) ratio. Subsequently, NP was partially replaced with nano-SiO2 in the selected mix to enhance the properties further. Fresh properties, such as, setting time of alkali-activated pastes (AAP) and the workability in terms of flow of mortar were determined. Evolution of compressive strength of concrete cured at 60 °C was monitored. Scanning electron microscopy (SEM) and X-ray diffration (XRD) were utilized to determine the morphology and mineralogy of the AAP, respectively. In addition, FTIR was used to identify functional groups formed in the AAP. The study reveals that a SS/SH ratio of 2.5 was suitable in achieving superior strength. AAC prepared using NP and nano-SiO2 exhibited improved strength and microstructural characteristics. However, 5% nano-SiO2 showed significant enhancement in the compressive strength and microstructural characteristics as compared to those prepared with other replacement levels. Consequently, the results of this study provides important information on developing NP-based sustainable building material with remarkable enhancement in the properties by adding nano-SiO2.

Effect of alkaline activators and binder content on the properties of natural pozzolan-based alkali activated concrete

The stringent conditions are being imposed by the global community to reduce greenhouse gas emissions, will push the search for low carbon footprint alternative binders to ordinary Portland cement. In this pursuit numerous studies have been carried out to synthesize alkali activated concrete (AAC) utilizing industrial by-products, such as, fly ash that is rich in silica and alumina. Natural Pozzolan (NP) is one of such alternative cementitious materials having desirable chemical compositions that could be potentially used to develop AAC. The present work focuses on the effect of curing period, composition of alkaline activators and binder content on the properties of natural pozzolan-based AAC. A total of 15 AAC mixes were prepared by varying the sodium silicate to sodium hydroxide (SS/SH) by weight ratio from 2.0 to 2.75 and binder content between 350kg/m3 and 450kg/m3. Fresh properties, such as, setting time of alkali activated pastes (AAP) and workability of concrete were determined. Compressive strength was measured on the specimens cured for 0.5, 1, 3, 7, 14 and 28days in an oven maintained at 60°C. For selected mixtures, scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques were utilized to study the morphology and mineral composition of the developed alkali activated paste (AAP), respectively. Additionally, FTIR was used to identify functional groups formed in the AAP. The results showed that the composition of alkaline activators and binder content have significant effect on the properties of AAC. Considerable strength gain was recorded after 3days of curing and further curing up to 7days improved the strength. However, continued curing up to 28days marginally decreased the strength. Further, SS/SH ratio of 2.5 and binder content of 400kg/m3, resulting in alkaline activators to binder ratio of 0.525, was found to be suitable for achieving superior strength and microstructural characteristics.