Sludge Ash Research Articles

Application of paper sludge ash and incinerated sewage ash in emulsified asphalt cold mixtures

Certain disadvantages could have appeared while using hot mix asphalt (HMA), such as the release of unhealthy gases into the environment (environmental issues), difficulty in sustaining the temperature over long distances (logistical issues), and consuming a sufficient amount of energy while preparing and laying down (practical and economic issues). To overcome the aforementioned issues, this study aimed to develop rapid-curing emulsified asphalt cold mixes (EACM) comprising a cementitious filler made from industrial by-product materials. Paper sludge ash (PSA) is used as an active filler for application in the EACM rather than conventional mineral filler. Additionally, to maximize the effect of PSA’s hydraulic activity, incinerated sewage ash (ISA) is utilized as an activator at a concentration of 0%–4% by mass of the aggregates. The results demonstrate that the use of waste PSA significantly improves the indirect tensile stiffness modulus (ITSM) by around 10 times more after 2 days than the traditional emulsified asphalt cold mixes. In addition, the improvement in ITSM was around 30% and 65% for 6%PSA+1%ISA and 6%PSA+4%ISA mixes, respectively. Furthermore, the rutting for the 6%PSA+1%ISA and 6%PSA+4%ISA mixes decreased to around 19% and 11% in comparison to the traditional 131-pen HMA. The formation of hydration products and rapid demulsification of asphalt emulsion, which results in binding within the mixtures, are responsible for the increased ITSM and rutting resistance. As a result, environmental issues are minimized, and energy preservation may be maintained.

The Influence of Sewage Sludge and Fly Ash Fertilization on the Total Number of Bacteria (TNB) and Bradyrhizobium Species in Soybean Agroecosystem

The aim of this study was to determine the impact of different chemical properties in soil, including changes in magnetic susceptibility and the impact of humic substances from sewage sludge and fly ash on the microbial community in the soybean agroecosystem. A field experiment was carried out using the random plot method on Cambisol with a texture of silt loam. The experiment consisted of 24 plots (six treatments and four replications) using different dozes of sewage sludge and fly ash. The following physicochemical and chemical analyses were performed in the soil samples: pH in KCl, conductivity (λ), total content of heavy metal, magnetic measurements and fractional composition of organic matter. The TNB and the number of the species of Bradyrhizobium in the field cultivation of the soybean variety Lissabon were evaluated using the spread plate method. The total content of heavy metals (Cu, Zn, Cd, Ni, Pb, Cr, Hg, Fe) in the analyzed treatments showed a significant difference between them. The study of the magnetic parameter χ indicated a significant differentiation between treatments from 34.0 to 65.8 × 10−8·m3·kg−1. High correlation coefficients between χ and Fe (r = 0.789), Zn (r = 0.653), Cr (r = 0.617) and TOC (r = 0.949) indicated that the source of these elements was external organic matter. Biological tests (TNB and species of Bradyrhizobium) in different experimental treatments indicated significant relationships between them and showed the resistance of the microbial community in the field cultivation of Lissabon soybean to heavy metal contamination from sewage sludge and fly ash. The study confirmed that external organic matter, such as sewage sludge, can be used as an alternative to natural fertilizers for soybean production.

Study on adsorption of hexavalent chromium by composite material prepared from iron-based solid wastes

A new adsorbent with chromium removal function was synthesized by carbon thermal method using iron-containing waste Fenton sludge and carbon-containing solid waste fly ash to treat high pH scoring wastewater generated from industrial processes. The results showed that the adsorbent used T = 273.15 K, pH = 10, t = 1200 min, C0 = 100 mg/L, had a removal rate of Cr(VI) of more than 80%, and the adsorption capacity could reach 393.79 mg/g. The characterization results show that the synthesized mesoporous nitrogen-doped composite material has a large specific surface area and mesoporous structure, and the surface of the material is rich in oxygen-containing functional groups and active sites. Compared with other studies, the adsorption capacity of the material is larger, which indicates that the removal effect of Cr(VI) in this study is better. The adsorption kinetic results show that the adsorption follows a pseudo second kinetic model, and the adsorption process is a chemisorption involving electron sharing or electron exchange. This experiment designed a simple method to synthesize mesoporous nitrogen-doped composites using industrial solid waste, with raw materials from cheap and easily available industrial solid waste, and solved the dual problems of heavy metals in wastewater and solid waste, providing a new idea for the resource utilization of Fenton sludge while not producing secondary pollution.

Phosphorus Recovery and Simultaneous Heavy Metal Removal from ISSA in a Two-Compartment Cell

Traditional acid extraction or electrodialytic remediation (EDR) is inefficient to recover phosphorus (P) from incinerated sewage sludge ash (ISSA). This study used a hybrid process including acid extraction and EDR to extract P from ISSA and remove heavy metals/metals from the P extract sequentially. Specifically, the P extract was obtained by extracting ISSA with 0.2 M H2SO4 and a two-compartment cell was applied in the following EDR process. Constant currents of 15 mA, 35 mA and 50 mA were applied for the electromigration of the heavy metals/metals. Results showed that the efficiency of heavy metals/metals removal fluctuated and was relatively low (approximately 20%) under a current of 15 mA. Increasing the current to 35 mA significantly increased the removal efficiency and that of 50 mA was conspicuous, except Fe, Al and As (<50%). Meanwhile, P gradually immigrated to the catholyte after an EDR duration of 96 h. Consistent with heavy metal/metal immigration results, the pH change and 50 mA voltage drop were dramatic (the pH change was 12 and the voltage drop was 11 V). In addition, flocculent precipitates, which were predominantly Ca, P, Al, Mg and Fe, were found in the catholyte.

MECHANICAL STRENGTH OF MATERIALS APPLIED IN SOIL STABILIZATION

Road works and other civil works involve large amounts of materials and earth movements that could be minimized with the best use of material from the construction site itself, through the process of improving the soil obtained from the union with materials able to add resistance. This is because, when the soil is loaded, it tends to deform and this disturbance alters the load flow of the structure, modifying the effort value achieved in the project. For these reasons, the objective of this work was to analyze the mechanical resistance of materials applied in the improvement and stabilization of soils. Therefore, knowing the lineage of this theme, this study was developed with the intention of identifying, in the literature, consistent treatments that favor the inheritance of soil resistance. This is an integrative review carried out on scientific data sources: Scientific Electronic Online Library (SciELO) and Google Scholar. Searches for studies were carried out from August to December 2022. The descriptors selected to search for data were: road works, soil improvement and soil stabilization. The inclusion criteria for the selection of scientific articles were: articles published from 2001 to 2017, in Portuguese; monographs, theses, dissertations, available and complete articles. Exclusion criteria were: publications of repeated articles in databases.To implement soil stabilization, many issues need to be persistent, in the study one of them was that the cement presents stable performance in soil stabilization, reaching SSI rates above 80% for base according to DNIT. As well as the alternative materials, they present the values for application in base and subgrade, with the superior capacity of 2% of ISC for the subgrade when applied with sludge ash and lime reaching the guidelines for use in the base.

Environmental impact of recycling sewage sludge into cementitious matrix: A review

This paper reviews the literature associated with the impact of disposed sewage sludge at the environment and the possibility of recycling sewage sludge into sustainable constructional material. The rapid population growth in India has led to increased demand for drinking water and thereby resulted in the discharge of an enormous quantity of sewage. Globally, the total sewage generation has been higher than the total sewage treatment capacity. Additionally, stringent norms for sewage disposal in surface waters have made it imperative to develop proper infrastructural facilities, and increase the amount of operational sewage treatment plants (STPs). The adoption of physico-chemical treatment processes for the treatment of raw sewage generates higher volumes of sewage sludge. Plant operators face serious challenges in the disposal of the generated sludge, i.e., the requirement of larger disposal areas, higher handling & transportation costs, environmental (groundwater, air, and soil) contamination because of the heavy metals' leaching from the disposed sludge, etc. Hence, the paper includes options for recycling sewage sludge ash (SSA) as a substitute for some of the cement used to make concrete. The present review study aims to understand the impact on the characteristics of the cementitious matrix due to the incorporation of sewage sludge. Also, the study has attempted to identify various mineral admixtures that are expected to enhance the properties of concrete containing sewage sludge. The basic information provided in the paper would help researchers assess the suitability of reusing waste materials containing both organic and inorganic compounds. The decision to reuse waste sewage sludge would depend on whether this waste constituent could compromise the strength of the sustainable cementitious matrix or contribute to releasing toxic constituents from this matrix owing to a high leachability.The scientific committee of the International Conference on “Technological Interventions for Sustainability (Chem-Conflux22)” was held at The Motilal Nehru National Institute of Technology Allahabad, Prayagraj, on April 14th − 16th, 2022, oversight abstract selection and peer-review.

Experimental analysis of strength and durability properties of cement binders and mortars with addition of microfine sewage sludge ash (SSA) particles

Generation of sewage sludge is increasing all over the world, and its safe disposal is becoming a serious concern. Utilization of this waste as a raw material for some products can lead to multiple advantages. Considering the physical and chemical properties of the sludge, it can be used as a replacement for cement as its properties are similar to those of cement. Moreover, the sludge is being incinerated for better workability. The purpose of this study is to utilize supplementary cementitious materials like sewage sludge ash as a replacement for cement for better properties like strength and durability. Incorporating such waste materials into concrete can reduce the use of cement, making it eco-friendly. During this investigation, the water-cement ratio was kept constant at 0.5. Different percentages (5,10,15,20,25) of microfine Sewage Sludge Ash (SSA) a being used as a replacement for the cement. Tests conducted during this analysis are compressive; setting time, rapid chloride permeable test (RCPT) and XRD (for the detection of the occurrence of crystalline material). The results show that the compressive strength of the mortar at 10% is higher than that of 20%. Cement binders and mortars could benefit from the usage of this waste material because it has a significant impact on their strength and durability.

Petroleum sludge ash-derived MCM-41-silver nanocomposites for enhanced photocatalysis and antimicrobial effect in water treatment

This study introduces a cost-effective methodology to synthesize Ag@MCM-41 composites, utilizing petroleum sludge ash as a precursor.

Repair mortars with water treatment plant sludge (WTPS) and sugarcane bagasse ash sand (SBAS) for more eco-efficient and durable constructions

Water treatment plant sludge (WTPS) and sugarcane bagasse ash sand (SBAS) can be used as fine aggregate in cementitious composites. This paper aims to evaluate carbonation depth, chloride penetration, steel corrosion probability, and corrosion rate of cementitious repair mortars produced with 3% WTPS and 30% SBAS. The results showed SBAS mortars have the best performance in relation to carbonation and chloride penetration tests. WTPS mortars have similar results to the reference sample. Both mixes with by-products were able to provide a more protective environment for steel reinforcement. They presented a delayed steel corrosion probability of 25% (for 3WTPS) and 113% (for 30SBAS) in comparison to the reference sample. This is due to increased alkalinity and refinement of pores given by incorporation of fine waste materials. Moreover, 3WTPS and 30SBAS can significantly reduce corrosion rates of steel reinforcement in the order of 70% and 97%, respectively. Therefore, 3WTPS and 30SBAS composites can be satisfactory used in jacketing repair mortars for more eco-efficient and durable constructions.

Performance and microstructure of sustainable cementitious materials mixed by municipal sewage sludge ash, slag, and fly ash

Substituting cement with sewage sludge ash greatly benefits the environment and the economy, but the improved methods of the performance of sludge ash cementitious materials should be further studied. Systematic experiments were designed to investigate the effects of typical municipal sewage sludge ash (SSA) in combination with slag and fly ash on cementitious material properties, including workability, mechanical strength, water absorption, chloride penetration, and drying shrinkage. Furthermore, the hydration and microstructure of the cement pastes were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and nitrogen adsorption and desorption (NAD) tests to better understand the properties of sludge ash cementitious materials. The results demonstrate that, 30 wt% SSA resulted in 18.6 % fluidity loss, 16.01 % lower compressive strength, and higher water absorption coefficient and chloride migration coefficient (DRCM) at 28 days compared with the reference specimen. However, the performance of the sludge ash mortar was improved with the combination of SSA, slag, and fly ash. The optimum combination proportion was found to be 10 wt% SSA, 10 wt% fly ash, and 10 wt% slag, and the corresponding mortar demonstrated ideal strength and resistance to water absorption and chloride migration. Additionally, the mortar with 30 wt% SSA had more than 30 % reduced drying shrinkage compared to the reference cement mortar at 90 days. The slag converted monosulfate into hemi/monocarboaluminate, thus increasing the abundance of hydrates, and the incorporation of slag and fly ash promoted pozzolanic reactions and refined the pore structure of the blended pastes. This study proposes a reliable and practical method to promote the utilization of sludge ash.

Adsorption Characteristics of Phosphate Based on Al-Doped Waste Ceramsite: Batch and Column Experiments.

Phosphorus widely existing in rainfall and wastewater impacts the water environment. In this study, sludge, cement block, and coal fly ash were employed as ceramsite material to synthesize Al-doped waste ceramsite (Al-ceramsite) for removing phosphate (PO43--P) from aqueous solutions. Batch static adsorption-desorption experiments were designed to investigate the effect of various parameters such as Al-ceramsite dosage, PO43--P concentration, temperature, initial pH, coexisting ions, and desorbents on the removal of PO43--P. Also, the fate of PO43--P removal efficiency in actual rainwater was studied through dynamic adsorption column experiments using Al-ceramsite. Results showed that Al-ceramsite could remove PO43--P efficiently under the optimum parameters as follows: Al-ceramsite dosage of 40 g/L, initial PO43--P concentration of 10 mg/L, temperature of 25 °C, and pH of 5. Besides that, the Al-ceramsite could completely remove PO43--P in actual rainwater, and the effluent PO43--P concentration was lower than the environmental quality standards for surface water Class Ⅰ (0.02 mg/L). The adsorption characteristics of Al-ceramsite on PO43--P by X-ray photoelectron spectroscopy (XPS) were further explained. As a result, ligand exchange and complexation were confirmed as the main PO43--P removal mechanism of Al-ceramsite. Thus, Al-ceramsite was prepared from industrial waste and has shown excellent potential for phosphorus removal in practical applications.

Production of sorptive granules from incinerated sewage sludge ash and upcycling in cement mortar

This paper describes a method to produce sorptive granules solely from solid waste. The produced granules can remove multi-toxic heavy metal(loid)s from wastewaters and be upcycled as lightweight aggregates in cement mortars. Specifically, kilogram-scale production of millimeter-sized granules was obtained via the thermal treatment of green bodies prepared from phosphorus-stripped incinerated sewage sludge ash (ISSA), peanut shell and waste bentonite at a mass ratio of 1:1:2 at 1050 °C under a N2 atmosphere. The synthesized granules with good mechanical strength (4.9 MPa) exhibited excellent adsorption capacities towards As(V), Cr(VI), Cu(II) and Pb(II) at respectively 14.11, 5.79, 14.12 and 23.52 mg/g at an initial solution pH of 3.0 via mechanisms including redox reactions, complexation, (co)precipitation, and cation exchange. Moreover, the potentially hazardous spent granules could be environmental safely reused as a partial river sand replacement in cement mortars based on the Toxicity Characteristics Leaching Procedure.

The development of an eco-friendly cold mix asphalt using wastewater sludge ash

The aim of this research was to develop a sustainable and ecologically sound, non-traditional cold mix asphalt (CMA) that can be used in the construction industry. This new type of CMA incorporates wastewater sludge fly ash (UFA) and bottom ash (UBA) as a replacement filler for ordinary Portland cement and limestone. Silica fume (SF) was also used as an additional filler. The mechanical and durability characteristics of the new CMAs were examined in terms of indirect tensile stiffness modulus (ITSM), and rutting, fatigue, water and fuel resistance. The results showed that CMA with 2.1% OPC +3.9% UFA at 3 days of age, had ITSM values 11 times that of traditional CMA, while CMA with 2.1% OPC+ 3.3% UFA +0.6% UBA, had ITSM values 5 times that of traditional CMA at 28 days of age. SF activated hydration for both mixes, significantly increasing ITSM. These results indicate that CMA has a comparable mechanical performance to standard Hot Mix Asphalt (HMA) mixtures for use as surface pavement layers. This study offers a novel CMA with improved mechanical performance. It is economically effective and ecologically beneficial, compared to HMA, due to its ability to accommodate wastewater sludge ashes that are often disposed of in landfill sites.

Modelling and optimization of sewage sludge composting using biomass ash via deep neural network and genetic algorithm

In this study, the use of Deep Cascade Forward Neural Network (DCFNN) was investigated to model both linear and non-linear chaotic relationships in co-composting of dewatered sewage sludge and biomass fly ash (BFA). Model results were evaluated in comparison with RSM, Feed Forward Neural Network (FFNN) and Feed Back Neural Network (FBNN), and Cascade Forward Neural Network (CFNN). DCFNN produced predictive results with MAPE values less than 1% for all datasets in all experimental designs except one with 1.99%. Furthermore, the decision variables were optimized by Genetic Algorithm (GA). The desirability level obtained from the optimization results was found to be 100% in a few designs and above 95% in all other designs. The results showed that DCFNN is a reliable and consistent tool for modeling composting process parameters, also GA is a satisfactory tool for determining which outputs the input parameters will produce in an experimental setup.

Kinetic and Equilibrium Isotherm Studies for the Removal of Tetracycline from Aqueous Solution Using Engineered Sand Modified with Calcium Ferric Oxides

The novel aspect of this research is the fabrication, characterisation, and application of an engineered adsorbent made from quartz sand coated with calcium ferric oxides (QS/CFO) derived from the wastepaper sludge ash (WPSA) for the removal of tetracycline (TC) from synthetic water. Initially, the new adsorbent was fabricated using a Ca/Fe molar ratio, sand/FeCl3 ratio, pH (of synthesising environment), ethylene glycol dose, and temperature of 1:0.75, 1:1, 12, 6 mL/100 mL, and 95 °C, respectively. Then, the new adsorbent was applied to treat water having 50 mg/L of TC in batch experiments, taking into account the effects of the contact time (0–180 min), pH of water (2–12), the dose of adsorbent (0.05–0.5 g), and agitation speed (0–250 rpm). The results obtained proved the engineered adsorbent can remove as much as 90% of the TC (adsorption capacity of 21.96 mg/g) within 180 min at an initial pH, adsorbent dosage, and agitation speed of 7, 0.3 g per 50 mL, and 200 rpm, respectively. It was also found that the pseudo-second-order model describes the kinetic measurements better than the pseudo-first-order model, which indicates that the TC molecules have been bonded with the prepared sorbent through chemical forces. Furthermore, the intra-particle diffusion model results demonstrated that the diffusion mechanism plays a significant role in TC adsorption; however, it was not the predominant one. Finally, the outcomes of the characterisation analysis proved that the newly formed layer on the quartz sand substantially contributed to the removal of the TC from the contaminated water.

Pyrometallurgy treatment of electroplating sludge, emulsion mud and coal ash: ZnAlFeO4 spinel separation and stabilization in calcium metasilicate glass

Electroplating sludge was a hazardous waste comprised of heavy metals and other Fe/Al/Ca/Si impurities, and produced massively in surface treatment industry. In the past, it was commonly purified via hydrometallurgy, chlorination and reduction calcination routes, but also blended as additive in rotary kiln, to stabilize the heavy metals in geopolymer. Herein, an alternative strategy was developed to treat a real electroplating sludge for recycling magnetic Zn-rich spinel and stabilizing Zn in calcium metasilicate glass via a facile pyrometallurgy route with the blending of emulsion mud and coal ash. The sludge contained 35.6% Zn and 0.54% Cr and then was blended with 50% emulsion mud. After calcination at 1200 °C, the product was highly dispersed, whilst octahedral ZnAlFeO4 spinel with Zn content of 40.0% were formed and separated by using magnet, in accordance with the recycling efficiency of 51.2% Zn from the electroplating sludge. But after calcination at 1400 °C, the gypsum in emulsion mud was decomposed as CaO and accelerated the dissolution of Si-bearing substance as calcium metasilicate glass for covering ZnAlFeO4 spinel, resulting in the Zn leaching of 1568 mg/L. By adding 50% Si-rich coal ash in the calcination system, more calcium metasilicate glass were generated, and then the Zn concentration in the toxic leaching test was only 12.09 mg/L. During the calcination, Cr showed similar performance to Al/Fe and involved in the spinel formation. This provided a new route to recycle Zn from Zn-rich electroplating sludge and to solidify heavy metals via calcium metasilicate glass route.

Hydration mechanism and environmental impacts of blended cements containing co-combustion ash of sewage sludge and rice husk: Compared with blended cements containing sewage sludge ash

In this study, the hydration mechanism and environmental impacts of blended cements with the co-combustion ash of rice husk and sewage sludge (CCA) were investigated and compared to those of blended cements with sewage sludge ash (SSA). CCA possesses lower phosphate contents than SSA, leading to lower inhibition effects on early hydration of cement clinker. Moreover, the pozzolanic activity of CCA is higher than that of SSA. Thus, more hydration products from the pozzolanic reaction of CCA are generated in CCA-based blended cements. Compared to the matrix of SSA-based blended cements, that of their CCA-based counterpart is filled with more hydration products, which promotes porosity refinement and strength development of CCA-based blended cements at later ages. CCA-based blended cements exhibit greater environmental benefits than SSA-based blended cements because fossil consumption and toxic substance emissions during the co-combustion of rice husk and sewage sludge is lower than that during the mono-combustion of sewage sludge.

Chromium-containing wastewater reclamation via forward osmosis with sewage sludge ash temperature-sensitive hydrogel as draw agent

A temperature-sensitive hydrogel modified with sewage sludge ash (SSA) was used as an advanced draw agent for forward osmosis (FO) application in treating chromium-containing wastewater. The performance of the modified hydrogel (SSA-TSH) was measured in terms of the swelling and deswelling properties, as well as adsorption and desorption effects on Cr(VI), chemical oxygen demand (COD), total phosphorous (TP) and ammonium (NH4+-N) in chromium-containing wastewater. Furthermore, the efficiencies of wastewater treatment, water flux, and the reusability of the SSA-TSH as draw agent in the FO process (FO-SSA-TSH) using a commercially available thin-film composite membrane (Sterlitech) were also investigated. The results indicated that FO-SSA-TSH achieved high removal rates of pollutants (Cr(VI): 96.9 %–97.4 %, COD: 97.1 %–97.4 %, TP: 97.7 %–99.6 %, and NH4+-N: 76.8 %–77.9 %) in various Cr(VI) concentrations (0– 40 mg/L) due to the high rejection rate of FO membrane and notable adsorption capacity of the hydrogel. Moreover, the average water flux of FO-SSA-TSH (1.95– 2.02 LMH) was nearly twice as much as that of the FO with pure temperature-sensitive hydrogel as draw agent (FO-TSH, 1.33– 1.42 LMH) in 24 h chromium-containing wastewater treatment. In addition, SSA-TSH with excellent deswelling property exhibited high water recovery performance and good reusability in low cost and energy consumption after the FO permeation process for wastewater treatment.

Effect of Alum Sludge (AS) and Palm Kernel Ash (PKA) with Coconut Shell as Partial Replacement of Aggregates

At present, there is a high demand for concretes with varying properties. Generally, concrete with high durability can be produced by considering the constituents of the concrete, such as cement, sand, aggregates, and water. The quality of concrete is also dependent on the mix design and production method, such as transporting and pouring of concrete. In recent years, the developed countries have been focusing on the issue of sustainability in construction to create a healthier environment and reduce the environmental impact of a building throughout its lifetime while optimizing its economic viability and ensuring the comfort and safety of the occupants. One way to achieve sustainability is using agricultural waste material such as palm oil fuel ash, rice husk, fly ash slag, sludge, and coconut shell in concrete production. This study performs a series of tests to investigate the effect of using alum sludge (AS) and palm kernel ash (PKA) with coconut shells as a partial replacement of aggregates. The concrete samples were subjected to compressive strength, flexural strength, rebound hammer, ultrasonic pulse velocity, water permeability, water absorption, carbonation, alkali-silica reaction, SEM, and shrinkage tests.

Hydration mechanism and phase assemblage of ternary blended cements based on sewage sludge ash and limestone: Modified by Na2SO4

This study developed an eco-friendly ternary system based on sewage sludge ash and brought in Na2SO4 as a modifier to increase the mechanical property. The changes of the hydration kinetics, microstructure and phase assemblage of the ternary system with the addition of Na2SO4 were investigated. The results show that Na2SO4 accelerates the hydration kinetics of the ternary system and promotes the reaction of both clinker and sewage sludge ash, leading to the increase in compressive strength. The formation of the aluminate phases is promoted by the addition of Na2SO4, which contributes to porosity refinement and strength development. Moreover, Na2SO4 modifies the composition and microstructure of the aluminate phases in the ternary system. The addition of Na2SO4 promotes the formation of carboaluminate phases due to the increase in the alkalinity of the pore solution, which reflects on the appearance of the third hydration peak in the heat flow curves. However, with the increase in the addition level of Na2SO4, the formation of carboaluminate phases is inhibited due to the fact that the aluminates react preferentially with sulfate rather than limestone.