Basic properties, durability and microstructure of alkali-activated hemihydrate phosphogypsum incorporating with ground granulated blast furnace slag (GGBFS)

Recycling of heavy metal contaminated river sludge into unfired green bricks: Strength, water resistance, and heavy metals leaching behavior – A laboratory simulation study

Radiological characterisation of alkali-activated construction materials containing red mud, fly ash and ground granulated blast-furnace slag

Mechanical strength, water resistance and drying shrinkage of lightweight hemihydrate phosphogypsum-cement composite with ground granulated blast furnace slag and recycled waste glass

Research on hydration characteristics of OSR-GGBFS-FA alkali-activated materials

As the building sector is expanding, a growing interest in technologies that can reduce the CO2 emission from concrete production has led to partial replacement of cement with by-products from various industrial processes. Besides the partial replacement of cement, development of alkali activation technology ensures full replacement of cement in concrete. Although alkali activated materials (AAMs) are one of the most sustainable alternatives to cement-based concrete, structural application of AAMs is still not viable, as their long-term performance is not sufficiently studied. For instance, no recommendations are yet given to the scientific and engineering communities as a general approach for testing carbonation of AAMs. Furthermore, there is a limited number of case studies of long-term performance of AAMs in the past to assist the predictive models of their service life. The long-term performance (carbonation resistance) of AAMs is mainly dependent on the microstructure features of the binder (e.g. phase assemblages and pore structure), which can be modified using different constituents and materials mixture designs. Therefore, the aim of this thesis was the development of a conceptual carbonation mechanism that can be applied to analyse carbonation resistance of any alkali activated concrete mixture. For this reason, the carbonation mechanism was studied at different length scales, from paste to concrete level, while the effects of carbonation on the chemical, physical and mechanical properties were captured. The relationship between carbonation rate, pore solution chemistry and microstructure was investigated. An advanced microstructure characterization of fly ash (FA) and ground granulated blast furnace slag (GGBFS) was performed using PARC software. The combined effect of GGBFS content, curing (sealed/unsealed) and exposure conditions (natural indoor/outdoor and accelerated carbonation) on the carbonation resistance of pastes was considered. Based on the parameter studies (GGBFS content, curing, exposure conditions), recommendations for design of alkali activated concrete for engineering practice are given in view of carbonation resistance.

Experimental Study and Numerical Simulation of the Reaction Process and Microstructure Formation of Alkali-Activated Materials

By reutilizing industrial byproducts, inorganic cementitious alkali-activated materials (AAMs) contribute to reduced energy consumption and carbon dioxide (CO2) emissions. In this study, coal gangue (CG) blended with ground granulated blast furnace slag (GGBFS) was used to prepare AAMs. The research focused on analyzing the effects of the GGBFS content and alkali activator (i.e., Na2O mass ratio and alkali modulus [SiO2/Na2O]) on the mechanical properties and microstructures of the AAMs. Through a series of spectroscopic and microscopic tests, the results showed that the GGBFS content had a significant influence on AAM compressive strength and paste fluidity; the optimal replacement of CG by GGBFS was 40-50%, and the optimal Na2O mass ratio and alkali modulus were 7% and 1.3, respectively. AAMs with a 50% GGBFS content exhibited a compact microstructure with a 28 d compressive strength of 54.59 MPa. Increasing the Na2O mass ratio from 6% to 8% promoted the hardening process and facilitated the formation of AAM gels; however, a 9% Na2O mass ratio inhibited the condensation of SiO4 and AlO4 ions, which decreased the compressive strength. Increasing the alkali modulus facilitated geopolymerization, which increased the compressive strength. Microscopic analysis showed that pore size and volume increased due to lower Na2O concentrations or alkali modulus. The results provide an experimental and theoretical basis for the large-scale utilization of AAMs in construction.

The potential of copper slag as a precursor for partially substituting blast furnace slag to prepare alkali-activated materials

This study investigates the durability and microstructural characteristics of concrete incorporating sustainable materials. Lime and ground granulated blast furnace slag (GGBFS) are used as partial replacements for cement, while granulated blast furnace slag (GBFS) and recycled coarse aggregate (RCA) are used to replace natural fine and coarse aggregates. Durability performance is evaluated by sulphate attack, rapid chloride permeability, water sorptivity, carbonation and fire resistance tests. Microstructural properties are examined using X-ray diffraction, scanning electron microscopy, Fourier transform infra-red spectroscopy and thermogravimetric analysis. A total of 11 concrete mixes were prepared, including a control mix without additives, one mix with 60% GGBFS and nine mixes containing different combinations of 50, 75 and 100% GBFS and RCA, along with 6% lime and 60% GGBFS. The use of GGBFS improves durability by reducing the amount of free calcium hydroxide and filling the concrete pores. However, increasing GBFS and RCA content tends to reduce durability due to their relatively weaker properties. Microstructural analyses support these trends. Three mixes among nine mixes exhibit superior or comparable durability as compared to the control concrete, highlighting their potential for promoting sustainable concrete production, reducing waste and supporting the circular economy in construction.

This paper investigated the heat evolution of pastes containing inert and active materials with different particle sizes. Ground river sand was used as an inert material while ground granulated blast furnace (GGBF) slag was used as an active material. Ground river sand (GRS) and GGBF slag were ground to have the same particle size and were used separately as a replacement of Portland cement type I at rates of 50 – 70 % by weight of the binder. Heat evolution of pastes containing GRS and GGBF slag was measured using an isothermal conduction calorimeter up to 72 h. The results showed that GRS with different particle sizes had a slight effect on the heat evolution of pastes. GGBF slag with median particle size d50 of 4.4 µm and d50 of 17.8 µm had a small effect on the heat evolution of pastes during the first 24 h, and the pastes also had very low heat evolution for up to 72 h. At the same replacement rate of Portland cement, however, the heat evolution due to the slag reaction was slightly increased when the particle size of the GGBF slag was decreased. Finally, the higher is the cement replacement by GGBF slag, the higher is the slag reaction.DOI: http://dx.doi.org/10.5755/j01.ms.23.1.13579

Alkali-activated materials are low-environmental-impact binders that can be obtained from the alkaline activation of industrial wastes. In this study, converter steel slag as the major raw material and ground granulated blast furnace slag (GBFS) as the modified material were activated by water glass with a modulus of 1.5 and a Na2O dosage of 4%. The hydration process, microstructure and compressive strength of alkali-activated composite materials were investigated. The results show that adding GBFS accelerates the initial dissolution of the particles, leading to higher first exothermic peaks. But adding GBFS decelerates the formation of hydration products, resulting in the delay of the second exothermic peaks. Adding GBFS has no significant effect on the cumulative hydration heat, Ca(OH)2 content and the type of gel in the alkali-activated steel slag systems. However, with increasing GBFS content, the Ca–Si ratio in the gel decreases, and the Al–Si ratio increases. Adding GBFS can refine the pore structure and produces more Si–O–Si bonds in gels, resulting in a significant increase in the compressive strength. The improvement effect of GBFS on the compressive strength is more obvious at a later stage than at an earlier stage.

Commonly used alkali activation precursors such as blast furnace slag and fly ash will soon become less available due to resource competition, and may cease to be produced in certain regions. This limitation in future supply is a main driving force for the investigation of alternative precursor sources, such as non-blast furnace slags and non-ferrous slags, to produce alkali-activated binders. The current study investigates the incorporation of copper slag (CS) and stainless steel slag resulting from electric arc furnace operations (EAFSS) as partial replacements for ground granulated blast furnace slag (GGBFS) in producing alkali-activated materials (AAMs), at paste level. Five binary alkali-activated mixtures with different replacement levels of GGBFS with CS, and three ternary mixtures with both CS and EAFSS as partial and total replacements for GGBFS, are activated by a sodium silicate solution. Replacing GGBFS with CS and EAFSS retards the reaction kinetics, resulting in improved fresh-state properties of the investigated AAMs, better retention of workability and longer setting times. The reaction of alkali-activated 100% CS shows minimal initial exothermic activity until 3.5 h, when a single intense peak appears, representing delayed dissolution and subsequent polycondensation. X-ray diffraction (XRD) data indicate that the main crystalline phases of CS and EAFSS are stable in these alkaline systems; it is the glassy components that react. The use of CS and EAFSS in blended AAMs causes a minor increase in porosity of ~ 1–3% with respect to GGBFS only, and a small reduction in compressive and flexural strengths, although these reach 80 MPa and 8 MPa, respectively, after 28 days, even at a replacement level over 65 wt. %. Conversely, the 100% CS mixture exhibits a one-day compressive strength of 23 MPa, with a negligible increase thereafter. This result agrees with both FTIR and SEM analysis which highlight only minor changes in binder development after two days. It is believed that the unusual behaviour of CS in the investigated mixtures is related to the low availability of calcium in this precursor material.

The replacement of natural resources in the manufacture of cement and sand is the present issue in the present construction scenario. Copper slag and Ground Granulated Blast furnace Slag (GGBS) are industrial by-product materials produced from the process of manufacturing copper and iron. Use of Copper slag and GGBS does not only reduce the cost of construction but also helps to reduce the impact on environment by consuming the material generally considered as waste product. Hence in the current study an attempt has been made to minimize the cost of cement and sand with concrete mix grade M25 by studying the mechanical behavior of this concrete mix by partial replacing with advanced mineral admixtures such as Copper slag and GGBS in concrete mix. In this study, partial replacement of Cement with GGBS and Sand with Copper Slag considered. Experimental study is conducted to evaluate the workability and strength characteristics of hardened concrete, properties of concrete have been assessed by partially replacing cement with GGBS, and sand with Copper Slag. The cement has been replaced by GGBS accordingly in the range of 0% (without GGBS), 5%, 10%, 15%, and 20% by weight of cement for M25 mix. The sand has been replaced by Copper slag accordingly in the range of 0% (without Copper slag), 10%, 20%, 30%, and 40% by weight of cement for M25 mix. Concrete mixtures were produced, tested and compared in terms of compressive, flexural and split tensile strength with the conventional concrete. Keywords - Copper slag, GGBS, Workability, Compressive strength, Split tensile strength, Flexural strength.

Formulation and characterization of blended alkali-activated materials based on flash-calcined metakaolin, fly ash and GGBS

Manufacturing of portland cement is an energy-intensive process and releases a large amount of greenhouse gases into the atmosphere, which affects the earth’s ecosystem. Efforts are being carried out to conserve energy by means of promoting the use of industrial wastes like Ground Granulated Blast Furnace Slag (GGBS), silica fumes, flyash, etc., which show chemical properties similar to cement. Replacement with industrial waste products like GGBS, flyash, silica fume, etc. which are having pozzolanic property same as cement will help to reduce the rate of cement consumption. This study evaluates the mechanical properties of concrete with Ground Granulated Blast-furnace Slag (GGBS). In the GGBS based concrete, cement was replaced with GGBS ranging from 60% to 80% and the specimens were cured with water/CO2 gas curing. Carbon Dioxide gas curing is an advanced curing process for cementitious material that provides strength at an early stage of the curing process, also known as an accelerated curing technique. Concrete when combined with Carbon Dioxide gas as a curing agent under specified temperature, pressure and duration gives an early strength at a short period of curing time. The curing of the concrete specimens was performed with water for 28 days/CO2 gas for 6 and 12 hours. The addition of CO2 as a curing agent for the concrete specimens also results in the production of more ettringite and C-S-H gel in the concrete. It also shows a huge amount of calcium hydroxide and the C-S-H hydration product under Scanning Electron Microscope (SEM) images. This study reveals that curing with CO2 gas gives better compressive and flexural strength at an early age for concrete mix with high volume GGBS than ordinary cement concrete.