Slag-based Cement Research Articles

Comparison of Phosphogypsum-Steel Slag-Based cement and Portland cement for stabilization of heavy metals in oil-based drillings cuttings

This research compared Portland cement and Phosphogypsum-Steel Slag-Based (PSSB) cement in terms of their capabilities to stabilize heavy metals (specifically lead and nickel) in Oil-Based Drill Cuttings (OBDC). In the experimental section, the qualitative analysis of heavy metal constituents in OBDC was captured by X-ray Photoelectron Spectroscopy (XPS). Additionally, an acetic acid leaching test was implemented for the heavy metal leaching concentration to evaluate the ceramsite stabilization effect on OBDC. In the simulation phase, cement models, heavy metal ion models, and stabilization models were constructed to explore the stabilization mechanism of heavy metals. Results demonstrated that PSSB cement exhibits superior stabilization effects on OBDC compared to Portland cement. Flame Atomic Absorption Spectrophotometry (FAAS) tests showed that PSSB cement reduced Ni and Pb leaching by 21.87 % and 47.32 %, respectively, compared to Portland cement. In PSSB cement, the diffusion coefficients for Ni and Pb ions were observed to decrease by 42.92 % and 79.63 %, respectively, as revealed through Mean Square Displacement (MSD) analysis. The cohesive energy of PSSB cement was 76.73 % lower than that of Portland cement, and its interaction energies for stabilizing Ni and Pb ions were 59.43 % and 76.22 % lower, respectively, demonstrating greater stability and efficiency in metal stabilization. PSSB cement exhibited lower heavy metal concentration and better structural stability than Portland cement.

Experimental Investigation on Strength, Durability and Micro Structural Characteristics of Slag-Based Cement Mortar

Experimental Investigation on Strength, Durability and Micro Structural Characteristics of Slag-Based Cement Mortar

Physical-chemical coupling excitation of low activity coal gasification slag solid waste and its application as a backfill cementitious material

To realize the green mining and clean utilization of coal resources, environmental issues such as coal mine subsidence and coal gasification slag (CGS) solid waste storage require urgent resolution. High residual carbon and low activity serve as bottlenecks for CGS to achieve safe, efficient and resourceful consumption. Therefore, in this study, we proposed the concept of graded utilization of CGS and conducted a study on physical–chemical coupling to stimulate the hydration activity of CGS. We prepared a modified coal gasification slag-based cement paste backfill material (MCGS-CPB) to meet the technical requirements of coal mine backfilling. Through various experimental tests and microscopic characterization methods (uniaxial compressive strength, hydration heat and microscopic tests, etc.), we elucidated the modification mechanism of CGS, and the synergistic reaction law of MCGS-CPB was clarified. The following results were obtained. (1) The best excitation approach for CGS hydration activity was salt modification, and the early strength of MCGS-CPB prepared with CGS excited by sodium sulfate (SS) developed rapidly, while the later strengths showed expansion and deterioration. The strength development of MCGS-CPB prepared by CGS activated with calcium chloride (CC) was relatively stable, and the excitation effect was ideal. (2) The salt modification of CGS had a significant effect on the early hydration process of MCGS-CPB. The durations of the initial dissolution, acceleration, deceleration and slow reaction stages were prolonged, and the duration of the induction stage was shortened, while the hydration heat release rate increased. (3) The salt modification of CGS had a significant effect on the microstructure of MCGS-CPB, primarily due to the difference in excitation effect of salt modification on CGS on pozzolanic activity. This study provided theoretical guidance for the safe, efficient and resourceful utilization of CGS.

Durability, mechanical properties and rebar corrosion of slag-based cement concrete modified with graphene oxide

The application of nanomaterial to concrete is an innovative approach to enhancing mechanical properties and durability. In fthis work, the combined additions of graphene oxide nano-platelets (GO) to concrete mix formulated to use ground granulated blast furnace slag (GGBFS) as a substitute for Portland cement (PC) for use in salt-rich environments is studied. The need arises in both off-shore structures and also places coming to contact with brine due to de-icing of road structures or the geological peculiarities specific to saline terrain. The physical, mechanical, chloride, and water permeability and electrical conductivity tests on the developed concrete are compared with those of ordinary concrete under conditions of varying temperature and water pressure. The addition of GGBFS is known to improve the mechanical properties of concrete specimens. Results from the present work show that the addition of no more than 0.1 wt% GO to 50 wt% GGBFS substituted concrete increases the after-curing compressive strength by 40 %, and flexural strength by 60 %. The electrical conductivity of the 90-day cured samples as a measure of chloride permeability dropped from nearly 4000 Coulombs in ordinary concrete to roughly 1100 Coulombs for the modified concrete indicating a nearly 70 % reduction. Accelerated CSH gelation, followed by Ca(OH)2 crystallization after GO addition, combined with altered pore structure from the addition of finely milled slag. The nucleation mechanism is affected such that the average pore diameter falls to 6.2 nm from 11.4 nm in the PC concrete. The low porosity thus established is reflected in the measured improvements in strength, resistance to water absorption, chloride permeability, and the overall enhanced corrosion performance. Calorimetric conductivity, thermogravimetric analysis (TGA), and differential thermogravimetric (DTG) analysis under nitrogen from 105 to 1000 ◦C, total porosity and pore size distribution using Mercury Intrusion Porosimetry (MIP) with a maximum pressure of 200 MPa, X-ray diffraction, linear polarization and electrochemical impedance spectroscopy (EIS) corrosion test results further corroborate that the addition of 0.1 % by weight of GO improved the physical, durability, and corrosion resistance properties of GGBFS concrete.

Pozzolanic Effect on the Hydration Heat of Cements Incorporating Fly Ash, Obsidian, and Slag Additives

Made up of an engineered mix of ordinary Portland cement (OPC) with artificial pozzolans such as trass, fly ash, and slag, the blended cements have been intensely employed within cementitious materials. The main reasons behind this intensive use can be clarified by enhanced workability/strength, the high resistance to chloride/sulfate, reduced permeability/alkali-silica reaction, and a drop in the heat generated by cement’s hydration. The use of cementitious blends within concrete not only offers durable products but also cuts climate impact by energy saving and falling CO2 emissions. This study presents pozzolanic effect on the hydration heat of cements incorporating fly ash, obsidian, and slag additives. The blended cements were manufactured by three different replacement ratios of 20%, 30%, and 50%. The change in the hydration heat of obsidian-, fly ash-, and slag-based cements was observed by several Turkish standards (TS EN 196-8 and TS EN 196-9). Mortars were used for determining the uniaxial strengths of obsidian-, fly ash-, and slag-based cements. The results show that cement’s hydration heat decreases as the rate of additives (e.g., obsidian) increases from 20% to 50%. The cement’s fineness greatly affects its hydration heat. Increasing the refinement of pozzolanic material to a certain level (30%) leads to an increase in the hydration temperature. After reaching this level, there is no clear relation between the fineness and the replacement rate of pozzolans. As a result, the findings of this work will provide a good understanding of artificial pozzolans on performance and quality of obsidian-, fly ash-, and slag-based cements.

Thermal conductivity and shrinkage properties of slag-based cement concretes

The thermal conductivity, specific heat, and total drying shrinkage test of slag blended OPC cement is conducted by using a Hotdisk-2500S thermal conductivity, and non-contact shrinkage deformation measurement apparatus based on ISO 22007-2 and GB/T50082-2009 test standards, respectively. The influence of replacement rates of slag cement (0, 30, 50, and 70%) and high-temperature exposure (21, 200, 400, 600, and 800 °C) on the thermal properties of concrete is analysed. The results show that for all three concretes, the thermal conductivity initially decreases with increasing temperature up to 400 °C, then after it remains almost constant between 400 and 600 °C, and gradually begins to decrease again up to 800 °C. Furthermore, thermal diffusivity of concrete group G-70, shows 21.4, 21.6, and 37.6% increment in 21, 200, and 600 °C temperature exposure respectively compared to concrete group G-0. Though, as the exposure temperature keeps rise to 800 °C, its value starts to decrease. Furthermore, the results indicated that high volume slag cement content in the concrete mix lessen the drying shrinkage of the concrete at later age. Test data is used as a function of temperature and slag replacement to establish high temperature relations for thermal properties. The proposed thermal property relationships can be used as input data for validation in computer programs and to evaluate the response of OPC and slag blended Portland cement concrete structures subjected to fire.

A fractal-based approach for reconstructing pore structures of GGBFS-blended cement pastes

The durability and mechanical behavior of cementitious materials can be substantially affected by changes in pore structure that occur during the hydration process. An accurate analysis of pore structure thus plays an important role in the interpretation and prediction of the performance of cementitious materials. This study investigated an analytical fractal reconstruction procedure for cementitious materials and demonstrated its application by reconstructing pore structure using fractal theory from a geometric perspective. For this purpose, microstructural characteristics of ground granulated blast-furnace slag-based cement pastes were evaluated using the results of mercury intrusion porosimetry measurements. Fractal characteristics in the mesopores and larger capillary pores were quantified using the pore surface fractal type, whereas those in the middle capillary pores were quantified using the solid mass fractal type. As a result of reconstructing pore structure, variations in the cumulative pore volumes appeared similar to those of the measured pore structure. Moreover, the differential pore size distributions of all pore regions were quantified as the fractal dimensions. These results indicated that the investigated methodology can be practically applied for the analysis of changes in pore structure caused by hydration in cementitious materials.

Carbonation resistance of mortar produced with alternative cements

The use of alternative cements with lower CO2 emissions during production compared to ordinary Portland cement (PC) is only sustainable, if the durability and with it the service life of components and structures produced with them are not compromised. In this project, the carbonation resistance of mortars produced with calcium sulfoaluminate cement (CSA) and three different slag-based cements is studied in accelerated conditions and natural exposure. Additionally, the diffusion coefficients of oxygen ($$D_{{{\text{O}}_{2} }}$$) and carbon dioxide ($$D_{{{\text{CO}}_{2} }}$$) are measured (the latter one only on carbonated mortars) and the change in mortar porosity due to carbonation is determined. Mortar PC used as reference and mortar CSA display the lowest carbonation coefficients, both in accelerated conditions and natural exposure. The three systems based on slag display higher carbonation coefficients. After carbonation, the diffusion coefficient $$D_{{{\text{O}}_{2} }}$$ is increased for all mortars except for mortar PC, whose total porosity is decreased as well, in contrast to all other mortars. The diffusion coefficients $$D_{{{\text{O}}_{2} }}$$ and $$D_{{{\text{CO}}_{2} }}$$ show a linear relationship in the carbonated mortars.

Slag-Based Cements That Resist Damage Induced by Carbon Dioxide

The use of sodium carbonate as an activator to prepare alkali-activated cements from blast furnace slag and calcined hydrotalcite offers many attractive performance and environmental benefits. However, the understanding of the long-term performance of these cements is limited. In this study, the resistance of sodium carbonate-activated slag cements to carbonation attack was determined under natural (0.04%) and elevated (1.0%) CO2 concentrations. Two calcium carbonate polymorphs, calcite and vaterite, were formed as carbonation products at a longer time of CO2 exposure. A cross-linked alkali aluminosilicate gel and a Ca-deficient calcium (alumino)silicate hydrate gel were identified to form by decalcification of the main binding phases initially present in these cements. However, despite these carbonation-induced mineralogical changes, the mechanical strength after carbonation was comparable to that of noncarbonated specimens, which is contrary to previous observations of strength loss due to carbonation o...

Calcium Extraction from Blast-Furnace-Slag-Based Mortars in Sulphate Bacterial Medium

Wastewater structures, such as treatment plants or sewers can be easily affected by bio-corrosion influenced by microorganisms living in waste water. The activity of these microbes results in deterioration and can cause the reduction in structural performance of such structures. In order to improve the durability of mortar and concrete, different admixtures are being used and the best impact is observed in cement based materials combined with blast furnace slag. In this study, mortar samples with blast furnace slag were exposed to bacterial sulphate attack for 90 and 180 days. The leaching of calcium ions from the cement matrix and equivalent damaged depths of studied mortar samples were evaluated. The results showed more significant leaching of samples placed in bacterial environment, compared to the samples placed in non-bacterial environment. Similarly, the equivalent damaged depths of mortars were much higher for the bacteria-influenced samples. The slag-based cement mortars did not clearly show improved resistance in bacterial medium in terms of calcium leaching.

Evaluation of the damaged depths of slag-based mortars in aggressive sulphate conditions

Resistance of cement composites against various chemical processes such as sulphate attack and corrosion is nowadays one of the most desired property. Mechanism largely involved in sulphate corrosion is the ingress of aggressive ions through diffusion. The result of the ingress of aggressive ions is leaching of the elements from the mortar matrix and the deterioration of the composite. In the experiment, the slag-based cement mortars samples were exposed to an aggressive microbiological sulphate environment, represented by the bacteria A. thiooxidans, for the period of 6 months. The paper presents the investigation of damaged depths of cement mortars based on the leaching characteristics of the Ca ions. The damage depths (EDD) of cement composites were much higher (up to 0.2 mm) for samples placed in the biotic environment, which confirms the aggressive action of A. thiooxidans.

Stope depth effect on field behaviour and performance of cemented paste backfills

Cemented paste backfill (CPB) has been extensively used as a popular mine fill system for underground mining operations. Understanding the CPB’s in situ properties as an element of ground support is indeed really important for developing a well-organised mine design in terms of costs and security. In this paper, a comprehensive experimental work was conducted to better understand the effect of stope depth on in situ behaviour and performance of CPB having three different binding agents (ordinary Portland cement alone, slag-based cement and fly ash-based cement) over different curing times. A stope depth of 0 (it replicates the stope’s top), 5, 10, 15 and 20 m (it replicates the stope’s bottom) were virtually simulated by using an improved laboratory set-up, escorting with conventional plastic moulds. Results show that the highest compressive strength is obtained from CPB having slag-based cement. The strength of CPB increases with increasing stope depth mainly due to resulting improved geotechnical properties, such as reduced water content, degree of saturation and porosity as well as increased specific surface area retained at the bottom of a simulated stope. Geochemical testing shows that sulphate SO4−2 and calcium Ca contents increase with increasing curing time and reduce with increasing stope depth. As a critical point, a number of experimental relationships considered typically for different curing times, overburden pressure, arching stress and binder contents within CPB material were expressed and discussed.

Environmental impact analysis of blast furnace slag applied to ordinary Portland cement production

This study was conducted based on the ISO 14040/14044 standards to analyze the environmental impact caused by blast furnace slag utilization for ordinary Portland cement production in typical plants in Beijing. In addition, sensitivity analysis of resource consumption, transport distance, the allocation methods and life cycle impact assessment model were discussed in detail. The results showed that global warming potential and acidification potential were the most significant environmental impacts resulted by slag-based cement production, accounting for 58.5% and 21.7% of the total environmental impact, respectively. Moreover, the cement production and energy generation phases accounted for 66.6% and 29.6% of total environmental loads of slag-based cement from cradle to gate, respectively. Sensitivity analysis showed that the comprehensive environmental impact of slag-based cement was sensitive to the consumption of limestone and energy, as well as the allocation methods and life cycle impact assessment model; but was insensitive to the consumption and transport distance of blast furnace slag. Compared with traditional Portland cement, except for the approximately 9% increase of human toxicity potential, the other impacts of slag-based cement decreased to a certain extent. In particular, abiotic depletion potential and land use potential significantly reduced by 72% and 41%, respectively. Therefore, producing cement with blast furnace slag would slightly increase electricity consumption, but significantly improve the benefits of land resource and materials conservation and significantly decrease the comprehensive environmental impact of cement.

Thermodynamic modelling of alkali-activated slag cements

This paper presents a thermodynamic modelling analysis of alkali-activated slag-based cements, which are high performance and potentially low-CO2 binders relative to Portland cement. The thermodynamic database used here contains a calcium (alkali) aluminosilicate hydrate ideal solid solution model (CNASH_ss), alkali carbonate and zeolite phases, and an ideal solid solution model for a hydrotalcite-like Mg–Al layered double hydroxide phase. Simulated phase diagrams for NaOH- and Na2SiO3-activated slag-based cements demonstrate the high stability of zeolites and other solid phases in these materials. Thermodynamic modelling provides a good description of the chemical compositions and types of phases formed in Na2SiO3-activated slag cements over the most relevant bulk chemical composition range for these cements, and the simulated volumetric properties of the cement paste are consistent with previously measured and estimated values. Experimentally determined and simulated solid phase assemblages for Na2CO3-activated slag cements were also found to be in good agreement. These results can be used to design the chemistry of alkali-activated slag-based cements, to further promote the uptake of this technology and valorisation of metallurgical slags.

Life Cycle Analysis on Carbon Emission Reduction and Energy Saving by Using Slag as Alternative Materials in Cement Production

The carbon emission and energy consumption of using slag as a secondary raw material in cement production was quantified and analyzed in this study. Moreover, the carbon emission reduction and energy saving potential of slag-based cement (SBC) production were identified based on the comparative analysis between SBC and traditional Portland cement (TPC). The results showed that the carbon emission of SBC is about 6.73%, which was lower than that of TPC. Compared with TPC, the energy consumption of SBC is slightly increased by 2.05%. In addition, it was found that the combustion of coal and the power generation were the main sources for carbon emission in the life cycle of slag utilization, which account for 83.39% and 10.16% of the total carbon emission. Therefore, reducing the consumption of energy and increasing the recovery rate of waste heat in cement production were the most effective methods to improve the environmental performance of SBC. In addition, the improvement potential analysis was carried out for SBC. The results indicated that if the recovery rate of waste heat could reach to that of the international advanced level (15.6%), the carbon emission and energy consumption of SBC would be reduced by about 2.20% and 5.71%, respectively. If the proportion of renewable energy utilizationin power generation increased to that of the average international level, the carbon emission and energy consumption of SBC would be declined by 5.26% and 9.35% respectively.

Durability and compressive strength of blast furnace slag-based cement grout for special geotechnical applications

Special foundations, most prominently micropiles and soil anchors, are frequently used in construction today. In Spain, the grout for these special technical applications is generally prepared with portland cement, although the codes and standards in place stipulate only the minimum compressive strength required, with no mention of cement type. Those texts also establish a range of acceptable water:cement ratios. In the present study, durability and compressive strength in cement grout prepared with blast furnace slag cement at different w/c ratios are characterised and compared to the findings for a reference portland cement grout. The results show that slag grout exhibits greater durability than the portland cement material and complies with the compressive strength requirements laid down in the respective codes.

Study on Sulfate-Attack of Slag-Based Geopolymer Concrete

Geopolymer has been attracted world attention as a potentially revolutionary material that is one of the ideal substitutes of portland cement. Fundamental studies on geopolymer are increasing rapidly because of its potential commercial applications. However, little work has been done on its erosion resistance of sulfate. In this paper, slag and metakaolin as source materials, different modules of water-glass as activator were used to prepare slag-based geopolymer which was then prepared to make slag-based geopolymer concrete. Linear expansion rate and mass loss of concrete were used as indicators to explore different erosion rules of slag-based geopolymer concrete which was long-term immersed in the 5% ( by mass ) Na2SO4 solution. Comparative experiments were also done between slag-based geopolymer concrete and ordinary cement concrete. The results showed that geopolymer concrete had excellent sulfate resistance performance, linear expansion rate and mass loss rate of geopolymer were 0.024% and 0.58% respectively at the soaking age of 49d as the water glass modulus was 1.4 and the water-glass content was 4%. It was also found that the anti-sulfate ability of geopolymer concrete is much better than that of ordinary concrete with the same strength grade.

Sludge recycling within cemented paste backfill: Study of the mechanical and leachability properties

Cemented paste backfill (CPB) technology has become widely used in Canada and around the world. While most of the studies related to CPB have concentrated on the mechanical, physical, rheological and economical aspects, very few studies have been conducted on metal leachability. The objective of this study was to investigate the mechanical and environmental behaviour of a novel CPB technique consisting of incorporating various treatment sludges within the conventional paste mixture. For the CPB studied, the binder PC10-50 50/50 offers higher mechanical resistance than the slag-based cement. While PC-based binders are more or less penalized by the addition of sludge, slag-based cement benefits from this additive. In terms of leachability, the results show that PC and slag-based binders were efficient in minimizing the release of Zn and Mn even at a low binder proportion. The addition of 0.15% and 0.30% of three different sludges to the tailings paste backfill did not have any negative impact on metal leachability.