Air-Cured Alkali Activated Binders for Concrete Pavements

Nowadays very vast quantity of concrete is being used all over the world. Concrete is a mixture of cement, fine aggregate, coarse aggregate, and water. Fly ash, Copper slag, and GGBS are mechanical waste products in Coal, copper and iron industry respectively. Using this product, results in cost reduction of concrete and disposal solution of large waste products. In this review two combinations were taken and attempt was made to reduce usage of cement and sand content by saving cost of concrete and studied experimental behavior for strengths of M40 grade of concrete for combination of ground granulated blast furnace slag (GGBS) and Copper Slag (CS) and another combination of GGBS and Fly ash (FA). Experimental studies were performed on plain cement concrete and combination of GGBS and Copper Slag. Total 108 specimens were casted. In the first combination, four trial mixes were taken as maintaining GGBS 30% and varying Copper Slag by 10%, 20%, 30%, and 40% respectively. In second combination 4 trials were taken as maintaining fly ash 25% and varying GGBS by 40%, 50%, 60%, and 70%. A comparative analysis has been carried out for concrete in relation to Workability, Compression strength, Split Tensile strength and Flexural strength at 7,14,28 days with conventional concrete and two combinations. It was observed that replacement of cement by 30% GGBS and sand by 30% CS in combination 1 got maximum strength in all aspect than Conventional Concrete and combination 2.

The alarming rate of depletion of natural stone based coarse aggregates is a cause of great concern. The coarse aggregates occupy nearly 60-70% by volume of concrete being produced. Research efforts are on to look for alternatives to stone based coarse aggregates from sustainability point of view. Response surface methodology (RSM) is adopted to study and address the effect of ferrochrome slag (FCS) replacement to coarse aggregate replacement in the ordinary Portland cement (OPC) based concretes. RSM involves three different factors (ground granulated blast furnace slag (GGBS) as binder, flyash (FA) as binder, and FCS as coarse aggregate), with three different levels (GGBS (0, 15, and 30%), FA (0, 15, and 30%) and FCS (0, 50, and 100%)). Experiments were carried out to measure the responses like, workability, density, and compressive strength of FCS based concretes. In order to optimize FCS replacement in the OPC based concretes, three different traditional optimization techniques were used (grey relational analysis (GRA), technique for order of preference by similarity (TOPSIS), and desirability function approach (DFA)). Traditional optimization techniques were accompanied with principal component analysis (PCA) to calculate the weightage of responses measured to arrive at the final ranking of replacement levels of GGBS, FA, and FCS in OPC based concretes. Hybrid combination of PCA-TOPSIS technique is found to be significant when compared to other techniques used. 30% GGBS and 50% FCS replacement in OPC based concrete was arrived at, to be optimal.

Alkali-activated slag concrete: Fresh and hardened behaviour

Cement is the most significant component in concrete. Large scale manufacturing of cement consumes more energy and release harmful products (Carbon dioxide) into the atmosphere that adversely affect the environment and depletes the natural resources. A lot of research is going on in globally concentrating on the recycling and reuse of waste materials from many industries. A major share of research is focused on finding cementitious materials alternatives to ordinary Portland cement. Many industrial waste by-products such as quartz powder, metakaolin, ground granulated blast furnace slag, silica fume, and fly ash etc. are under investigations for replacement of cement in concrete to minimize greenhouse gases and improve the sustainable construction. In current research, the effects of a new generation, ultra-fine material i.e., alccofine which is obtained from ground granulated blast furnace slag are studied as partial replacement by 25% and with varying amounts of sulfonated naphthalene formaldehyde (i.e., 0.3%, 0.35% and 0.40%) on mechanical, water absorption, thermal and microstructural properties of concrete. The results showed moderate improvement in all concrete properties. Addition of SNF with combination of alccofine showed a significant enhancement in fresh, hardened properties and water absorption test as well as thermal and microstructural properties of concrete.

Behavior of alkali activated fly ash slag paste at room temperature

In the present scenario, there is a huge requirement of quality concrete for paver applications. The production of green and sustainable concrete has become a must to substitute the ordinary Portland cement (OPC) concrete. It is an eminent fact that the manufacture of OPC requires the burning of its raw materials which lead to a huge amount of carbon dioxide liberation; also, it requires a large amount of energy dissipation. The concrete produced using alkali activation has become renowned methods to replace the conventional OPC, which gives an answer to find a way to generate environmentally friendly concrete. In the current study, pavement quality concrete (PQC) is produced using alkali activation. The main focus of the work is to study the effect of powdered glass as a binding ingredient in Alkali-Activated Concrete (AAC) mixes. The alkaline activator used to activate the binder was sodium hydroxide solution dispersed in liquid sodium silicate. The utilization of industrial dissipate materials such as Ground Granulated Blast Furnace Slag (GGBS), fly ash, and waste glass powder was used as the binding ingredients, and stone crusher dust was used as fine aggregates. The experimental investigation showed that a PQC can be easily produced using alkali activation of industrial wastes satisfying its strength requirements. It was behaving better under fatigue, showing its relevance in usage as a pavement construction material.

The purpose of this experimental research is to investigate the properties of workability and strength of the concrete containing admixtures such as silica fume, fly ash, ground granulated blast-furnace slag, and rice husk ash. For this purpose, the workability and the strength of the concrete containing each admixture were tested and analyzed according to the unit weight of binder and the replacement ratio of each admixture. As a result, considering their workability and strength, the existence of minimum binder weight and optimum replacement ratio of concrete containing admixture to plain concrete were obtained for each admixture.

Expanding the world’s infrastructure drives up demand for building materials, particularly ordinary Portland cement (OPC) concrete, whose high carbon dioxide (CO2) emissions have a detrimental effect on the environment. To address this issue, researchers looked into employing alternative supplementary cementitious materials (SCMs), including metakaolin (MK), which is derived from calcined kaolin clay with pozzolanic properties, to partially or completely replace OPC in concrete. This review article examines the MK’s application in alkali-activated materials (AAMs) and OPC-based concrete. By interacting with calcium hydroxide, MK functions as a pozzolanic additive for OPC concrete, enhancing its mechanical qualities and durability. The use of MK as a source material in AAMs, a newly developed class of sustainable binders, is also covered in this article. The effects of different combinations of MK with additional SCMs, including fly ash (FA), ground granulated blast furnace slag (GGBFS), silica fume, and rice husk ash, on the characteristics of alkali-activated concrete both in its fresh and hardened states, are compiled. The majority of the articles considered in this study are from the past decade, while some relevant articles from 2014 and earlier are also taken into account. The results showed that adding MK to concrete in combination with FA or GGBFS has excellent synergistic effects on microstructural development, pozzolanic activity, and strength increases. In particular, the MK–FA mix demonstrated the most encouraging performance gains. Because of its large surface area, the use of nano-MK helped achieve a denser geopolymer structure and improve mechanical properties. The best curing temperatures for MK-based geopolymers to gain strength were found to be between 40 and 80°C for a total of 28 days. The review also pointed out that the compressive strength and geopolymerization process of MK-based geopolymers were enhanced by increasing the mass ratio of Na2SiO3 to NaOH and NaOH concentration. Nevertheless, geopolymerization was hampered by unnecessarily high alkali concentrations. Moreover, the compressive strength was increased by partially replacing MK with TiO2 or GGBFS. The synergistic effects of combining MK with other SCMs to improve concrete performance highlight the potential of MK-based solutions in lowering the environmental footprint of concrete buildings.

Alkali silica reaction (ASR) is influenced by external factors such as the surrounding environment of high alkalinity. Countries with cold climate have a high probability to be exposed to high concentrations of NaCl solution by the deicing salt. This condition will lead to serious ASR problems in concrete, if the aggregates contain reactive silica. The main research work in this paper is to investigate the effect of 15% replacement ratio of high quality fine fly ash (FA15%) and 42% replacement ratio of blast furnace slag (BFS42%) on the ASR mitigation in concrete with different alkali amount inside the pore solution. The experiments were conducted according to the accelerated mortar bars experiment following the JIS A1146 mortar bar test method. In addition, post-analysis such as observation of ASR gel formation by the Uranyl Acetate Fluorescence Method and observation of thin sections using a Polarizing Microscope were also conducted. The mortar bar tests show a very good mitigation effect of supplementary cementitious materials (SCMs). The results show that only small ASR expansions, which can be categorized as “innocuous”, occurred for specimens with 1.2% Na2Oeq using FA15% and BFS42%. However, larger alkali amount inside the system will require more SCMs amount.

High-performance concrete, besides aggregate, cement, and water, incorporates supplementary cementitious materials, such as fly ash and blast furnace slag, and chemical admixture, such as superplasticizer. Hence, it is a highly complex material and modeling its behavior represents a difficult task. This paper presents an evolutionary system for the prediction of high performance concrete strength. The proposed framework blends a recently developed version of genetic programming with a local search method. The resulting system enables us to build a model that produces an accurate estimation of the considered parameter. Experimental results show the suitability of the proposed system for the prediction of concrete strength. The proposed method produces a lower error with respect to the state-of-the art technique. The paper provides two contributions: from the point of view of the high performance concrete strength prediction, a system able to outperform existing state-of-the-art techniques is defined; from the machine learning perspective, this case study shows that including a local searcher in the geometric semantic genetic programming system can speed up the convergence of the search process.

Geopolymers are recognised for their environmental benefits and excellent chloride and sulfate resistance. However, information on the material characteristics and bond behaviour of geopolymers based on fly ash (FA) and slag is still relatively scarce. This paper presents a comprehensive study on the integration of two modern construction materials – geopolymer concrete (GPC) based on FA and ground granulated blast-furnace slag and glass-fibre-reinforced polymer (GFRP) bars. The aim of the study was to assist concrete structural design by identifying the key preparation parameters such as hardening and bond behaviour. It was found that the hardening of the GPC was much faster than that of ordinary Portland cement (OPC) concrete at an early age and the stress–strain curves, elastic moduli and splitting tensile strengths of the GPC were accurately predicted by existing models developed for OPC concrete. The GFRP bars in the GPC outperformed those in the OPC concrete in terms of normalised bond strength. The GPC reinforced with both GFRP and steel rebars exhibited similar bond–slip curves to the OPC concrete. Overall, the behaviour of the GFRP-reinforced GPC was found to be analogous to that of the OPC concrete while providing adequate compressive, tensile and bond strength for the construction of foundations of low-rise buildings.

Effects of elevated temperatures on properties of concrete containing ground granulated blast furnace slag as cementitious material

This study aims to predict the autogenous shrinkage of alkali-activated concrete (AAC) based on slag and fly ash. A variety of analytical and numerical models are available for the prediction of autogenous shrinkage of ordinary Portland cement (OPC) concrete, but these models are found to show dramatic discrepancies when applied for AAC due to the different behaviours of these two systems. In this study, a new numerical approach is developed to predict the autogenous shrinkage of alkali-activated slag (AAS) and alkali-activated slag-fly ash (AASF) concrete from the experimental results on corresponding paste. In this approach, the creep of AAS and AASF and the restraining effect of the aggregate are particularly considered. By this approach, a fairly good prediction is obtained. Moreover, the microcracking in paste caused by restraining aggregates is evaluated. The results indicate that AAC is subjected to high tendency of development of microcracking.

Effect of natural carbonation on the pore structure and elastic modulus of the alkali-activated fly ash and slag pastes

Performance of sustainable concretes containing very high volume Class-F fly ash and ground granulated blast furnace slag