High Sulfate Resistance Research Articles

Evaluating the use of harvested fly ash as a sustainable alternative in cementitious mixtures

This study investigated the feasibility of utilizing harvested fly ash from landfills and ponds as a sustainable alternative to traditional fly ash in cementitious mixtures. The research examined the fresh properties, compressive strength, dimensional stability, transport properties, alkali-silica reaction, and sulfate resistance of pastes, mortars, and concretes made with traditional class F fly ash (TFA) and two sources of class F harvested fly ash (HFA1 & HFA2). The results showed that the cementitious mixtures containing both traditional and harvested fly ash consistently exhibited superior performance across all properties compared to the reference mixture. Amongst the fly ash samples, the mixtures containing traditional fly ash (TFA) demonstrated the best performance, followed by HFA1 and HFA2.At 28 days, reference mortar showed 8–39 % higher compressive strength than fly ash mortars, while TFA-15, HFA1–15, and HFA2–15 mortars surpassed the reference strength by over 10 % at 90 days. TFA-15 mortar showed drying shrinkage of 259 microstrains, which was 10 % and 13.7 % lower than HFA1 and HFA2, respectively. At 30 % replacement, TFA’s shrinkage was 19 % and 26.4 % lower than HFA1 and HFA2. Water absorption in TFA, HFA1, and HFA2 mortars at 15 % replacement was 52 %, 41 %, and 21 % lower than the reference (C100) at 28 days. At 90 days, TFA-15 exhibited 44–49 % and TFA-30 showed 35–27 % reductions in water absorption before and after boiling, respectively, compared to 28 days. For resistance to chloride ingress, TFA, HFA1, and HFA2 concretes at 15 % replacement showed 228 %, 133 %, and 119 % higher resistance compared to C100, respectively. At 30 % replacement, TFA showed 142 % higher resistance, while HFA1 and HFA2 showed 39 % and 30 % higher resistance, respectively. In terms of sulfate resistance (SR) at 28 days, fly ash-containing concrete at 15 % cement substitution showed over 100 % higher SR than the reference concrete (C100). TFA-15 exhibited 26 % and 48 % higher SR than HFA1–15 and HFA2–15, while TFA-30 showed 35 % and 74 % higher SR than HFA1–30 and HFA2–30, respectively. In alkali-silica reaction tests, TFA-20 and HFA1–20 mortars reduced 14-day expansion by 86 % and 83 % below the 0.1 % threshold, and by 84 % and 76 % at 28 days, respectively, staying below the 0.28 % failure limit. TFA-15 reduced expansion by over 34 % and 40 % compared to HFA1–15 and HFA2–15 at 28 days, and by 55 % and 49 % at 30 % replacement.

Phase formation of oil‐well cements based on chemical industry wastes

AbstractThe crystalline compounds CaAl2O4 and Ca12Al14O33 are reliably identified by electron microscopic and X‐ray studies of the structural and phase features of clinker, and the iron‐ and chromium‐containing phases are presented in the form of solid solutions: Ca2Al0.48Fe1.52O5 and Ca5(CrO4)(CrO4)2. This allows creating of a heat‐resistant, strong, weighted oil‐well cement for cementing “hot” oil and gas wells. It has been found that obtained materials have enhanced strength – compressive strength after 28 days of setting reaches 55 MPa, quick‐setting – initial set – 2 hours 55 minutes, final set – 4 hours 20 minutes, quick‐setting – compressive strength after 3 days of setting reaches 48.6 MPa, bending strength reaches 6.7 MPa; and are hydraulic binders with water‐cement ratio of 0.17 – 0.38; with high sulfate resistance ratio of 1.31 which is 1.5 times higher than that of Portland cement.

Developing Geopolymer Concrete by Using Ferronickel Slag and Ground-Granulated Blast-Furnace Slag

Geopolymer concrete is gaining recognition as an environmentally friendly alternative to traditional cement-based materials, offering potential solutions for reducing the carbon emissions of the construction industry. This study aims to develop GGBFS–FNS geopolymers utilising ferronickel slag (FNS) and ground-granulated blast-furnace slag (GGBFS). Ground FNS (GFNS) is a potential candidate for replacing fly ash in geopolymers. This research aims to develop for the first time a GGBFS–FNS alkali-activated concrete. Numerous trials were conducted including different GGBFS–FNS blend percentages, several chemical admixtures and varying activator concentrations to develop the optimal binder mix composition. The effects of different chemical admixtures on the properties of geopolymer pastes, mortars, and concretes were investigated. The study evaluated setting time, compressive strength, shrinkage, and physical and durability properties. The results indicate that conventional admixtures have limited impact on the setting time, while increasing the water/solid ratio and decreasing the GGBFS content could extend the initial and final setting times. The presence of FNS aggregate could improve the compressive strength of geopolymer mortars. The water absorber admixture was highly effective in reducing shrinkage and increasing chloride diffusion resistance. The geopolymer mix containing 50 wt.% GFNS and 50 wt.% GGBFS with the presence of the water absorber admixture presented high chloride diffusion resistance, non-reactivity to the alkali–silica reaction and high sulphate resistance. Overall, the GGBFS–FNS geopolymers exhibited promising potential for engineering applications as an environmentally friendly material, particularly in aggressive environments.

Hydration characteristics, structure evolution of marine cement composites with high durability modified by colloidal nano-silica for low carbon footprints

The porous structure of cement composites provides channels for the invasion of chloride ions in marine environment, which limits their service life and low carbon footprints. Colloidal nano-silica (CNS) with the particle size of 10–30 nm theoretically can refine the pore structure, block the chloride ion transport channel. Thus, it is beneficial to improve the service life of cement composites and reduce the consumption of cement and carbon dioxide emission. In this paper, the CNS was introduced to partially replace high sulfate resistance Portland cement (HSRPC) preparing HSRPC-CNS composite. The hydration characteristics, strength property, porous structure and chloride ion resistance were investigated. The results revealed that the addition of CNS was effective in improving the properties of HSRPC-CNS composite, and the most suitable content of CNS was 3 wt%. In this case, the hydration process of HSRPC-CNS composite was accelerated, and the 28-days compressive strength increased by 12.26%. Additionally, as the CNS content increases to 3 wt%, the porosity and chloride diffusion coefficient decreased by 32.39% and 41.99%, respectively. Therefore, CNS can be used as a sustainable nano additive that improved compactness, alleviated chloride ion permeability and reduced carbon dioxide emissions in HSRPC-based composites.

Mechanical and durability properties of alkali-activated slag/waste basalt powder mixtures

There are several studies investigating the feasibility of basalt powder as a precursor in alkali-activated cement production. The originality of this research lies in investigating the mechanical and durability features of alkali-activated mortars manufactured by partially substituting granulated blast furnace slag (GBFS) with waste basalt powder (WBP). In this study, 20% of GBFS was replaced with WBP, and high temperature (300 °C, 600 °C, and 900 °C) and magnesium sulfate (5% concentration) resistance of the manufactured mortars were investigated. The deteriorations of the mortars subjected to high temperature and magnesium sulfate were examined by compressive strength test, ultrasonic pulse velocity test, scanning electron microscopy analysis, and Fourier transform infrared spectroscopy analysis. The compressive strength of the mortar produced with 20% WBP substitution was 9.9% lower compared to the mortar containing 100% GBFS as the precursor. However, the performance of alkali-activated slag (AAS), known for its good resistance to high temperatures, did not decrease with the WBP substitution. The reduction in strength of both mortars after 900 °C was approximately 86%. No excessive changes were observed in the visual appearance and the compressive strength of the mortars after 3 months of exposure to magnesium sulfate. Microstructure analyses also revealed that WBP substitution had a limited effect on the high temperature and sulfate resistance of AAS.

Effect of nano-silica on structure and properties of high sulfate resistant Portland cement mixed with mineral powder or fly ash

Hydrating-hardening properties of high sulfate resistance Portland cement (HSRPC) mixed with 35 wt% mineral powder (MP) or fly ash (FA) and the action mechanism of nano-silica (NS) under the condition of low-calcium hydrating phase were studied in this paper. Rheology, fluidity, setting time and compressive strength were investigated to explore the effect of NS on the basic physical properties of HSRPC doped with MP or FA. Mercury intrusion porosimetry (MIP), ultrasonic crack analysis, hydration heat and thermogravimetry (TG) were investigated to analyze the hardened structure and the hydration mechanism. The conclusions were as follows: For HSRPC with MP, the 0.1–0.5 wt% NS increased the yield stress, decreased the fluidity and prolonged the setting time. However, when NS content increased from 0.1 wt% to 0.5 wt%, the cumulative porosity increased by 9.8% and the 60 h (60 h) cumulative hydration heat decreased by 14.6% because NS with high specific surface area inhibited the hydration of HSRPC, but its particle filling increased the porosity of harmless pores to improve the 3day (3d) compressive strength slightly. After 28d of hydration, the compressive strength increased by 2.8%, ultrasonic amplitude increased by 19.3%, and calcium hydroxide (CH) decreased by 6.6%, indicating that NS fully reacted with CH generated by HSRPC hydration. For HSRPC with FA, the 0.1–0.3 wt% NS increased the yield stress, setting time and 3d compressive strength and decreased the cumulative porosity. The 60 h cumulative hydration heat increased from 155.9 J/g to 198.5 J/g. The ultrasonic amplitude of 28d hardened paste increased from 10.91 V to 17.01 V and the CH content decreased from 15.29% to 14.1%. It indicated that the 0.1–0.3 wt% NS with high activity reacted with CH and further promote cement hydration to generate a large number of hydration products to improve the densification and performance, especially at the early age.

Strength and durability of marine cement-based mortar modified by colloidal nano-silica with epoxy silane for low CO2 emission

The heavy use of marine concrete consumes a large amount of cement increasing CO2 emission. Improving the strength and durability of marine concrete is an effective strategy to reduce CO2 emission. This study aimed to introduce colloidal nano-silica (CNS) and epoxy silane modified colloidal nano-silica (M-CNS) to improve the mechanical performance and durability of High Sulfate Resistance Portland cement. Meanwhile, the CNS and M-CNS were incorporated to marine cement mortar, and the aggregation of CNS, and the hydration mechanism and micro-mechanism of the mortar were investigated. The results indicated that the workability, mechanical properties and durability of marine cement samples were enhanced with M-CNS addition. When adding 1 wt% M-CNS with grafting rate of 15% (M-CNS1), the chloride diffusion coefficient was reduced by 9.49% and the porosity was reduced by 18.84%. In addition, the compressive strength of cement mortar with M-CNS1 increased by 10.42%, 28.71% and 10.49% compared with blank specimens after curing for 3-, 7- and 28-days. The improvements in strength and durability indicate that M-CNS has a promising application for reducing CO2 emissions by marine concrete industry.

Long-Term Sulfate Resistance of Blended Cement Concrete with Waste Glass Powder

This study aimed to evaluate the long-term sulfate resistance of green concrete with blended cement at different waste glass powder contents. The used cement was blended with 10%, 20%, 40%, and 60% of waste glass powder. To benchmark performance, the X-ray diffraction (XRD) test was used to estimate the pozzolanic effect of glass powder, which exhibits a calcium hydroxide decrease. The concrete natural aggregates were replaced by 50%, and 100% with glass at 60% glass powder replacement. There was a direct relation between the concrete diffusion coefficient and the waste glass powder in blended cement. Results of compressive strength loss show a high sulfate resistance with waste glass powder content increasing in cement. Concrete with 50% glass aggregates produced a comparable enhancement in sulfate resistance to that produced with natural aggregates.

МОДИФІКОВАНІ СУЛЬФАТОСТІЙКІ ПОРТЛАНДЦЕМЕНТИ З ДОБАВКОЮ ЦЕОЛІТУ

The article shows that one of the ways to increase the sulfate resistance of cements is to use as an additive of pozzolanic action based on highly dispersed zeolite, which increases the corrosion resistance of concrete. Physical-chemical properties of zeolite tuff as a mineral constituent of Portland cements with the addition of pozzolana are presented. The use of modern grinding technology by separate grinding of Portland cement clinker and natural zeolite in mills with separators of the latest generation allows to obtain high quality Portland cement with zeolite CEM II/A-P 42.5 R PJSC "Ivano-Frankivsk Cement", characterized by high early strength. It is shown that the replacement of the clinker component with zeolite leads to a decrease the content of clinker minerals C3S and C3A in cements, which significantly limit the corrosion resistance of cement stone. Highly dispersed zeolite is characterized by increased pozzolanic activity (after 28 days, the absorption of Ca(OH)2 is 200-250 mg/g). Due to pozzolanic reaction with the formation of C-S-H-phases, the content of calcium hydroxide in the paste based on CEM II/A-P 42.5 R is reduced by 2 times compared to Portland cement CEM I 42.5 R. Decrease in the concentration of Ca(OH)2 in cement pastes eliminates the possibility of the formation of a significant amount of ettringite, which causes sulfate corrosion of cement stone. It was found that during the hardening of Portland cement CEM II/A-P 42.5 R under the influence of sulfate and magnesium media, the coefficient of corrosion resistance Ks after 56 days is 1.16 and 0.98, respectively, while for samples based on Portland cement CEM I 42.5 R Ks decreases by 1.2-1.3 times. The results of researches of influence of aggressive environments on corrosion resistance of Portland cement with the increased content of zeolite type CEM ІІ/В-Р 42.5 are resulted. For Portland cement CEM ІІ/В-Р 42.5 the coefficient of corrosion resistance in the conditions of sulphate environment Кс90 = 1.47. Portland cements with zeolite strength class 42.5, modified with superplasticizers of polycarboxylate type, are characterized by high sulfate resistance and should be used for the manufacture of concrete classes C25/30...C50/60 for construction of dams, hydraulic structures, sewers storage of waste from livestock farms, etc. Modified rapid-hardening Portland cements with the zeolite additive provide technical, environmental and economic effects in the manufacture of concrete and reinforced concretes of hydraulic structures.

Effects of natural zeolite and sulfate environment on mechanical properties and permeability of cement–bentonite cutoff wall

Cement–bentonite (CB) slurry cutoff walls are extensively utilized to restrict the horizontal flow of fluids. In this study, cement was replaced by four various contents of 0%, 10%, 20%, and 30% by natural zeolite to evaluate its effects on the unconfined compressive strength, flexural strength, tensile strength, and the coefficient of permeability of cement–bentonite–zeolite (CBZ) specimens. Since underground cutoff walls are always in danger of sulfate attack, the CBZ specimens were immersed in three different containers with three different pH values of 2, 5, and 8 to study the sulfate resistance of this material. Results have indicated that the strength of specimens decreases with an increase in zeolite content at early ages; however, increasing the amount of zeolite up to 20% improves the mechanical properties and permeability of cutoff wall materials at late ages. The bentonite/cement (B/C) ratio equal to 0.2 shows a relatively better response than B/C ratios equal to 0.14 and 0.3. Curing specimens in the sulfate environment increased the mechanical strength of specimens and decreased the coefficient of permeability at first ages. At the late ages, curing in sulfate solutions manifested disadvantageous effects on specimens; however, specimens containing zeolite indicated higher sulfate resistance than specimens without zeolite.

High Sulfate Resistance Portland Cement with Mineral Powder or Fly Ash in Marine Engineering: Effect of Nano-Silica on Structure and Properties and Mechanism Analysis Under Low-Calcium Conditions

High Sulfate Resistance Portland Cement with Mineral Powder or Fly Ash in Marine Engineering: Effect of Nano-Silica on Structure and Properties and Mechanism Analysis Under Low-Calcium Conditions

A Resource-Saving Process for Obtaining Sulfoferrite Clinkers and the Properties of Cements Made with Them Involving the Use of Metallurgical Waste

Processing of metallurgical raw materials — especially those with high concentrations of sulphur — is associated with huge amounts of waste, which can be used as the principal component in the production of materials for various industries. This paper describes the results of development work that dealt with high-reactivity raw mixes and the resource-saving production of cryoannealed sulfoferrite clinkers when natural and mining, metallurgical and chemical wastes are comprehensively used as components. The properties of cements made with the above waste components were also studied. It was found that high-grade cements can be obtained due to the hydraulic activity of cement mixes obtained from clinkers that were produced by annealing of optimum-composition three-component raw mixes containing limestone, phosphogypsum and hematite. The conducted study confirms that metallurgical waste can serve as an efficient material for the production of high-strength materials made with sulfoalumoferrite cements. The optimum parameters for the production of sulfoalumoferrite clinkers and cements made on their basis were found to be as follows: КН = 0.667, nS = 1.5–2.0 and the annealing temperature of 1,150–1,200 оС. The hydraulic activity of sulfoalumoferrite cements obtained from clinkers that were produced by annealing of optimum-composition three-component raw mixes containing limestone, phosphogypsum and hematite ensures that such cements are of M400 and M500 grades. The samples have a rather high strength, as well as high sulphate and wear resistance.

Sulfate resistance of eco-friendly and sulfate-resistant concrete using seawater sea-sand and high-ferrite Portland cement

The resource shortage of freshwater and river sand promotes the development of seawater sea-sand concrete (SWSSC). However, most of the previous studies of SWSSC focused on plain ordinary Portland cement (OPC) systems, the poor sulfate resistance of which is detrimental to the durability and sustainability development of SWSSC. High ferrite Portland cement (HFPC) has higher sulfate resistance, higher abrasion resistance, and low energy consumption and CO2 emission in comparison with OPC, thus providing a great alternative for SWSSC. Here, we investigate the sulfate resistance of SWSSC using OPC and HFPC. The deterioration process, the sulfate attack products, and the microstructure changes were analyzed by a series of macro and micro analysis. The results show that OPC concrete is seriously damaged with an 83.9% loss of strength. Seawater sea-sand can improve the sulfate resistance, which is mainly due to the refinement of pore structure and the consumption of erodible components. Moreover, compared with SWSSC using OPC, SWSSC using HFPC shows much better sulfate resistance, and the important role of Fe in increasing the stability of hydration products is revealed. Such findings contribute to an in-depth understanding of the deterioration mechanism and the improvement of sulfate resistance of SWSSC.

EXPERIMENTAL STUDY ON DURABILITY OF ROOM TEMPERATURE CURING UFC MORTAR

In recent years, as structures become higher, larger, and more durable concrete whose compressive strength of the concrete is 150 N/mm 2 or more have been put to practical use. It is for this reason that it is necessary to develop strengthening materials with equal or better performance. Furthermore, the development of high-performance concrete repair materials is carried out because demand to seismic strengthening and repair increases. In this study, considering these circumstances, it was conducted an experimental study with the aim of developing a repair material using room temperature curing UFC (R-UFC). A binder composition preparation of the R-UFC has excellent fluidity under pressure. It was achieved that high-grade thixotropy, high compressive strength, and high bending strength. It can also be sprayed continuously because of its high thixtoropy. It was confirmed that the sprayed thickness was reached to 20mm by one work. Durability of this R-UFC was investigated and it was confirmed the high sulfate resistance, small drying shrinkage and low salt permeability.

Effect of silica fume and nano-silica on hydration behavior and mechanism of high sulfate resistance Portland cement

The main focus of this study was to investigate the effect of silica fume (SF) and nano-silica (NS) on hydration behavior and mechanism of high sulfate resistance Portland cement (HSRPC), and were analyzed in terms of chemical shrinkage, setting time, compressive strength, rheology, pore structure, hydration heat, and hydration products. Experimental results showed that 5 wt% SF deepened the secondary hydration reaction of HSRPC, because calcium hydroxide (CH) produced by HSRPC hydrating effectively stimulated the pozzolanic activity of SF at later ages. Compared with HSRPC, the 28 d total porosity and CH content of HSRPC with 5 wt% SF respectively reduced by 6.1% and 4.4%. The corresponding compressive strength increased by 14.4%. 0.1–0.3 wt% NS moved up the acceleration period of the hydration and reduced setting time. Meanwhile, NS with high pozzolanic activity evidently increased chemical shrinkage and compressive strength at early ages. Compared with HSRPC, the 28 d total porosity of HSRPC with 5 wt% SF and 0.3 wt% NS reduced by 16.3%. The CH content in TG-DTG curve was reduced by 24.7%, which was consistent with the reduction of CH characteristic peak value. Therefore, in the later hydrating process, the synergistic effect of SF and NS significantly promoted the second hydration reaction.

Study on sulfate resistance behaviour of granite sand as fine aggregate in concrete through material testing and XRD analysis

Abstract To develop sustainable concrete, partial replacement of cement with silica fume, fly ash, GGBFS was attempted in addition to the replacement of river sand with granite sand at the proportions of 0%, 25%, 50%, 75%, and 100%. The investigation leads to the breakthrough of ideal Sulfate resisting concrete with optimal design mix consisting Granite sand 25% + river sand 75% + partial replacement of cement by 7.5% silica fume + 10% fly ash + 10% GGBFS. The analysis results with the Sulfate resistance through only a 12.2% reduction in the tested compressive strength for the optimum design. All other design mix considered for the study indicated with lesser Sulfate resistance varying from 13.2 to 17.1% of reduction in compressive strength. Conventional river sand with admixtures leads to decline in compressive strength from 40 to 33 N/mm2 however the optimum design mix as identified in the study resulted with the higher sulfate resistance. It is estimated that 2% total cost savings were achieved for the identified optimal design mix for the 1 m3 of conventional concrete. Total cost savings of 2% were achieved for the identified optimal design mix for the 1 m3 of conventional concrete based on the estimation. The goodness of fit using Chi-Square analysis has been carried out for the developed regression equation towards estimating the compressive strength for various design mixes resulted in a value of 0.82.

The effects on durability and mechanical properties of multiple nano and micro additive OPC mortar exposed to combined chloride and sulfate attack

This study aims to improve the resistance of Portland Cement mortar to a combined chloride and sulfate attacks by the partial replacement of cement with nano and micro Pozzolan Material. The durability of the OPC mortar mixes investigated using Pozzolans, Fly Ash (FA), Metakaoline (MK), Slag with nano additives namely, Nano silica (NS), Nano titania (NT) and Nano alumina (NA) separately and in combined form. After proper curing, they treated with aggressive chemicals 5%NaCl, 5% Na2SO4 and 5% NaCl–5%Na2SO4 and tested their compressive strength at shorter and longer duration (7–180 d). The results are compared among binary, ternary blend of OPC and also compound effect of all nano additives. Durability evaluation by adopting tests: electrical resistance, chloride permeability, mass changes before and after chemical treatment and the results are presented. The composites containing nano additives enhanced the durability, corrosion resistance and improved the micro structure. The morphological changes studied using SEM supported the pore structure improvement. The deterioration period lengthened in the hybrid composites especially the samples incorporated with 50% MK + combination of all nano materials at 5% each, showed better chloride impermeability, high sulfate resistance with minimum corrosion current.

Behavior of Specialty Binders Mixed with Seawater

Abstract In recent years, worldwide research has been facing the challenge of finding solutions able to decrease the environmental impact of cement and concrete production. Many strategies could be adopted in order to reach this goal, such as reducing the clinker factor in cement or producing alternative clinkers to portland clinker, in addition to the adoption of efficient water recycling processes in concrete production, thus reducing the consumption of natural resources. An interesting approach to implementing the different strategies is to develop concretes combining the use of cement and seawater, permitting a significant saving in fresh water consumption and offering an important benefit to countries that are facing a water shortage. Thanks to the recent technological improvement in the composite material sector, corrosion-free reinforcements have been successfully developed, thus proposing an alternative to steel rebars in concrete, especially in exposure conditions that are critical because of the presence of chloride, or even in combination with seawater. The use of a specialty binder based on an intrinsically low pH and a high sulfate resistance can be beneficial for the stability of the concrete and of the embedded glass-fiber–reinforced polymer rebars. This article compares the mineralogical and mechanical behavior of pastes and mortars containing (1) limestone portland cement, (2) sulfoaluminate cement and (3) a blend of the two, when mixed with seawater. Compressive strength and drying shrinkage tests were performed, and the results were interpreted on the basis of the microstructural data obtained through X-Ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC). The results suggest that the phase assemblage of the systems and, in particular, the equilibria among the different Al2O3-Fe2O3-monovalent anion (AFm)/Al2O3-Fe2O3-trivalent anion (AFt) minerals play a key role in the strength development mechanism.

Resistance of alkali-activated slag to sulphate attack and elevated temperatures

Thermal stability as well as sulphate resistance of alkali activated slag (AAS) pastes prepared from Ground Granulated Blast Furnace Slag (GGBFS) and 5% fly ash (FA)are examined. AAS pastes are accelerated using alkaline solution of sodium hydroxide with concentration 1, 1.5 and 2 M and sodium silicate with fixed concentration (0.28 mol/Kg).AAS pastes exposed to 5% MgSO4 solution and to high temperature (200, 400, 600 and 800 oC). The compressive strength, bulk density, total porosity, chemically combined water content and phase composition are determined in this study. Concentration of 2M NaOH with 5% FA promotes the best properties of AAS pastes that exhibit the highest resistance to firing up to 400oC by achieving the greatest compressive strength. However, AAS pastes activated by 2M NaOHgive a high sulphate resistance.

A composite cement of high magnesium sulphate resistance

This study investigates the magnesium sulphate resistance of chemically activated phosphorus slag-based composite cement (CAPSCC). Enough mortar specimens were prepared from phosphorus slag (80 wt.%), type II Portland cement (14 wt.%), and compound chemical activator (6 wt.%) and were exposed to 5% magnesium sulphate solution after being cured. Mortar specimens of both type II and V Portland cements (PC2 and PC5) were also prepared and used for comparison purpose. According to the test results, after 12 months of exposure, PC2, PC5 and CAPSCC exhibited 43.5, 35.2 and 25.2% reduction in compressive strength, 0.136, 0.110, and 0.026% expansion in length, and 0.91, 2.2, and 1.78% change in weight, respectively. Complementary studies by X-ray diffractometry and scanning electron microscopy revealed that CAPSCC has a very low potential for the formation of sulphate attack products, especially ettringite. The results confirm a high magnesium sulphate resistance for CAPSCC compared to PC2 and PC5.