Impact of Portland Cement Content on Alkali Activated Bottom Ash

This study explores the behavior of blended mortars of low reactive bottom ashes (BA) and ordinary Portland cement (OPC) in an alkaline solution. Mortar mixtures incorporating OPC with different replacement levels (0% to 30% mass) were studied. Isothermal conduction calorimetric analysis was studied and 28-and 60-day mechanical strength values were found. SEM images was used to identifies porosity structures at 28-day. Water absorption was also investigated. The results revealed different behaviors to low (OPC 2.5 and OPC 5) and moderated (OPC 10 and OPC 30) OPC content. Increase in percentage of Portland accelerated hydration kinetics. There is a second peak formation for moderated OPC content, associated with C-A-S-H gel formation. The partial replacement of bottom ash by OPC tend to reduce the absorption. There is a slower initial water absorption to low OPC content. This behavior is due the higher unreacted BA content, that works as a filler. Otherwise, the increase of water absorption for OPC content is due to the coexistence of Portland cement hydrates and alkali activated reactions

Study of a cement with low environmental impact from sulfoaluminate clinker and phosphogypsum

A possibilidade de utilizar resíduos industriais como matéria-prima de produtos para a construção civil vem a cada ano ganhando mais importância no aspecto ambiental e tem também criado novos desafios tecnológicos. Além de evitar a degradação das áreas onde os resíduos normalmente são depositados, a valorização dos subprodutos tem por efeito a redução do consumo de matérias-primas virgens. Este artigo descreve um estudo no qual o fosfogesso, gerado pelas indústrias de produção de ácido fosfórico, foi empregado na formulação de um cimento em substituição total à gipsita. Buscou-se formular um cimento com baixo impacto ambiental (BIA) composto de mínimas quantidades de clínquer e máximas de fosfogesso. O clínquer empregado foi o sulfoaluminoso, caracterizado por necessitar de maiores quantidades de sulfato de cálcio em relação ao cimento Portland. Seis composições foram estudadas, cujas quantidades de fosfogesso e clínquer variaram entre 70-95% e 5-30%, respectivamente. A performance do BIA foi avaliada quanto à resistência mecânica e ensaios de durabilidade em argamassa padrão (NF EN 196-1). As interações entre fosfogesso e clínquer foram investigadas através da difração aos raios X (DRX) e análise térmica diferencial (DTA). Na análise da argamassa padrão, com a proporção de 1:3 (cimento:areia), a formulação composta por 30% de clínquer e 70% de fosfogesso apresentou resistência mecânica superior a 20 MPa aos 28 dias.The possibility of using industrial residues as raw materials for construction products has increased its importance for the environment and has also created new technological challenges. This article describes a study in which phosphogypsum, a by product of the phosphoric acid manufacturing industry, has been used for producing cement as a replacement for gypsum. The aim was to develop a cement with low environmental impact, with minimal consumption of clinker and maximum use of phosphogypsum (calcium sulfate). The sulfoaluminate clinker was used, which requires larger quantities of calcium sulfate in relation to Portland cement. Six combinations of phosphogypsum and clinker were tested, ranging between 70%-95% and 30%-5%, respectively. The performance of the low environmental impact was assessed, in terms of mechanical resistance, and durability tests for the standard mortar. (NF EN 196-1). The interactions between phosphogypsum and clinker were investigated by using XRD and DTA techniques. In the analysis of the standard mortar, with a proportion of 1:3 (cement: sand), the proportion of 70% phosphogypsum and 30% clinker resulted in a compressive strength higher than 20 MPa after 28 days

Production of Synthetic Phosphoanhydrite and Its Use as a Binder in Self-Leveling Underlayments (SLU)

An experimental study was conducted to investigate the potential use of phosphogypsum (PG) to produce self-leveling underlayments. The study was designed in two stages. Initially a phosphoanhydrite (PA) was produced by heating phosphogypsum at temperatures of 350 °C, 450 °C, 550 °C, and 650 °C. Two periods of heating were applied (2 and 4 h). The formation of anhydrite was determined by thermogravimetric analysis (DTA-TG) and confirmed by X-ray diffraction (XRD). The results show that anhydrite II was obtained at temperatures above 450 °C, and at higher calcination temperatures the PA solubility was lower. In the second stage of this research, the PA was used in self-leveling underlayments as the main binder in the ternary system comprised of calcium sulfate, calcium aluminate cement, and Portland cement. Self-leveling mortar screeds produced using PA (550 °C/4 h) and PA (650 °C/4 h) showed the best performance in terms of mechanical strength and no degradation was observed after immersion and immersion-drying tests. The formation of ettringite, identified by scanning electron microscopy (SEM), may have contributed to these results. Morphological changes were studied using the scanning electron microscopy (SEM) technique

Development of Alkaline-Activated Self-Leveling Hybrid Mortar Ash-Based Composites

This study investigated the reactivity properties of self-leveling hybrid alkali-activated cements, such as ordinary Portland cement (OPC) and its residual precursors, coal bottom ash (BA), and rice husk ash (RHA). Due to the relatively low reactivity of BA, binary mixes were produced with OPC using contents of 2.5–30% in the treated BA samples. Furthermore, ternary mixes were prepared in proportions of 25%, 50%, and 75% with RHA as a replacement material for the OPC (mix with 90%:10% BA:OPC). For all of the mixes the spreading behaviors were fixed to obtain a self-levelling mortar, and dimensional changes, such as curling and shrinkage, were performed. Mortars with 30% OPC reached a compressive strength of 33.5 MPa and flexural strength of 7.53 MPa. A scanning electron microscope (SEM) and X-ray powder diffraction (XRD) were used to indicate the formation of N-A-S-H and a (N,C)-A-S-H gel, similar to the gel with trace of calcium. The best performance was achieved when the binary mix produced 10% OPC. A hybrid mortar of OPS-BA presented 10 times lower susceptibility to curling than an OPC mortar. The results showed that both ashes reduced the shrinkage and curling phenomena

Microstructure and properties of hybrid coal gangue-based alkali-activated cement

Addition of Portland cement in low-calcium aluminosilicate-based alkali-activated materials can provide rapid hardening at room temperature, thus modifying microstructure and mechanical properties. In the present study, the effect of Portland cement addition on alkali-activated materials, cured at room temperature, was analysed by mechanical strength test, FT-IR and electrochemical impedance spectroscopy. The results showed samples hardening at room temperature after 24 hours and compressive strength of 26 MPa (7 days) for 5% of OPC addition. Hybrid alkali-activated cements presented higher sorptivity and lower electrical resistance than alkali-activated cement without OPC addition which can be related to more connected pores. The analysis of EIS spectrum highlights continued formation of microstructure over the ages of alkali-activated cement and can be related to mechanical properties and sorptivity

Estudo de um cimento com baixo impacto ambiental (BIA) a partir do clínquer sulfoaluminoso e do fosfogesso

The possibility of using industrial residues as raw materials for construction products has increased its importance for the environment and has also created new technological challenges. This article describes a study in which phosphogypsum, a by product of the phosphoric acid manufacturing industry, has been used for producing cement as a replacement for gypsum. The aim was to develop a cement with low environmental impact, with minimal consumption of clinker and maximum use of phosphogypsum (calcium sulfate). The sulfoaluminate clinker was used, which requires larger quantities of calcium sulfate in relation to Portland cement. Six combinations of phosphogypsum and clinker were tested, ranging between 70%-95% and 30%-5%, respectively. The performance of the low environmental impact was assessed, in terms of mechanical resistance, and durability tests for the standard mortar. (NF EN 196-1). The interactions between phosphogypsum and clinker were investigated by using XRD and DTA techniques. In the analysis of the standard mortar, with a proportion of 1:3 (cement: sand), the proportion of 70% phosphogypsum and 30% clinker resulted in a compressive strength higher than 20 MPa after 28 days.A possibilidade de utilizar resíduos industriais como matéria-prima de produtos para a construção civil vem a cada ano ganhando mais importância no aspecto ambiental e tem também criado novos desafios tecnológicos. Além de evitar a degradação das áreas onde os resíduos normalmente são depositados, a valorização dos subprodutos tem por efeito a redução do consumo de matérias-primas virgens. Este artigo descreve um estudo no qual o fosfogesso, gerado pelas indústrias de produção de ácido fosfórico, foi empregado na formulação de um cimento em substituição total à gipsita. Buscou-se formular um cimento com baixo impacto ambiental (BIA) composto de mínimas quantidades de clínquer e máximas de fosfogesso. O clínquer empregado foi o sulfoaluminoso, caracterizado por necessitar de maiores quantidades de sulfato de cálcio em relação ao cimento Portland. Seis composições foram estudadas, cujas quantidades de fosfogesso e clínquer variaram entre 70-95% e 5-30%, respectivamente. A performance do BIA foi avaliada quanto à resistência mecânica e ensaios de durabilidade em argamassa padrão (NF EN 196-1). As interações entre fosfogesso e clínquer foram investigadas através da difração aos raios X (DRX) e análise térmica diferencial (DTA). Na análise da argamassa padrão, com a proporção de 1:3 (cimento:areia), a formulação composta por 30% de clínquer e 70% de fosfogesso apresentou resistência mecânica superior a 20 MPa aos 28 dias

Assessing the interactions of retarding admixtures and fine materials in long-term flowability of cement pastes

The incorporation of supplementary fine materials into mortars and concretes is a common strategy employed to enhance both their rheological and mechanical properties. While organic molecule-based admixtures are primarily utilized to regulate the setting time in pre-mixed concretes and mortars, their effects become more intricate in the presence of fine materials. This study delves into the interplay between flowability and setting times of cement pastes with 50 wt% of fines (basalt filler, fly ash and quartz filler) in place of cement and three organic admixtures at 0.5 % and 1.0 % (wt% of cement). The results unveil compelling insights: the incorporation of retarding additives proves notably advantageous, markedly decreasing viscosity and prolonging the initial stage of paste formation by as much as 305 h. Nevertheless, the efficacy of these additives diminishes significantly in the presence of fine particles, especially when utilizing basalt filler. This prompts an in-depth exploration into the intricate interactions transpiring between the fine materials and the setting retardants. The implications of these interactions underscore their pivotal role in refining the application of retarding additives in scenarios involving fine materials

Autonomous Self-Healing Agents in Cementitious Materials: Parameters and Impacts on Mortar Properties

The concept of self-healing materials and the development of encapsulated curing agents represent a cutting-edge approach to enhancing the longevity and reducing the maintenance costs of cementitious structures. This systematic literature review aims to shed light on the parameters involved in the autonomous self-healing of cementitious materials, utilizing various encapsulated healing agents such as pellets, granules, and capsules. This review also identifies and selects studies that offer additional insights into the efficacy of the self-healing process in cementitious materials and the influence of these specific encapsulated healing agents on the physical mechanical properties of mortars. This comprehensive approach provides a deep understanding of the interplay between self-healing and the physical–mechanical properties of mortars containing these encapsulated healing agents. The main findings indicate that the cement-to-sand ratio, characteristics of fine aggregates, and encapsulation methods significantly impact crack control, self-healing efficiency, and properties of mortar in both fresh and hardened states. The content of encapsulated healing agents within the cementitious matrix affects both the initial workability or flow and subsequent mechanical properties. While pellets coated with PVA film typically reduce workability in the fresh state and compressive strength, capsules coated with Portland cement and sodium silicate mitigate these effects and improve crack sealing in fresh and hardened states without compromising the self-healing capacity of cracks. The three-point flexural test has emerged as the preferred method for a pre-crack assessment over 28 days, with variations depending on the type of healing agent used. As noted in the literature, water has been identified as the optimal environment for autonomous healing. These findings underscore the potential of encapsulation techniques to enhance self-healing capabilities through the controlled release of agents within the cementitious matrix, thereby advancing the research on and development of intelligent construction materials and increasing the durability of cement-based structures

Effect of alkaline salts on calcium sulfoaluminate cement hydration

This work analyzes the effect of the presence of 5 wt.% of solid sodium salts (NaSO, NaCO, and NaSiO) on calcium sulfoaluminate cement (CSA) hydration, addresses hydration kinetics; 2-, 28-, and 90-d mechanical strength, and reaction product microstructure (with X-ray diffraction (XRD), and Fourier transform infrared spectroscopy, (FTIR). The findings show that the anions affect primarily the reactions involved. Ettringite and AH, are the majority hydration products, while monosulfates are absent in all of the samples. All three salts hasten CSA hydration and raise the amount of ettringite formed. NaSO induces cracking in the ≥28-d pastes due to posthardening gypsum and ettringite formation from the excess SO present. Anhydrite dissolves more rapidly in the presence of NaCO, prompting carbonation. NaSiO raises compressive strength and exhibits strätlingite as one of its reaction products.This study was partially supported by the Brazilian National Council for Scientific and Technological Development (CNPq) under projects 208380/2017‐5 and 151890/2020‐0, and CAPES. Financial support was also furnished by the Spanish Ministry of the Economy and Competitiveness and FEDER under research project BIA2016‐76466‐R and funding from BES‐2017‐082022. PhD. student Pilar Padilla‐Encinas thanks the Autonomous University of Madrid for the opportunity to complete her thesis in its Applied Chemistry program. The cement supplied by Heidelberg Cement Hispania is gratefully acknowledge