Ground Granulated Blast-furnace Slag Cement Research Articles

Effects of exposure sequence and GGBS cement replacement on performance of concrete subjected to carbonation and chloride ingress

In a variety of applications, such as in tidal zones, abutments of bridges and concrete tunnel linings, reinforced concrete is exposed to both carbonation and chloride ingress. The exposure can be either simultaneous or sequential. However, durability design rarely considers synergistic effects due to carbonation and chloride ingress, even though this may have detrimental consequences for performance. Comparative implications of exposure sequence across different concrete compositions are also unknown. In this study, an experimental investigation on the effects of the sequence of carbonation and chloride ingress was conducted, using two concretes which differ by 50% cement replacement with ground granulated blast furnace slag (GGBS). Specimens were exposed to a combination of 10% CO2 accelerated carbonation and immersion in 3% sodium chloride solution, in either sequence, and compared with companion samples subjected to only one of these aggressive environments. The extent of carbonation was measured using phenolphthalein indicator solution, while silver nitrate and Rapid Chloride Testing provided indicators of the chloride ingress. For both concrete mixes, specimens with prior chloride ingress exhibited a decreased rate of carbonation when compared to specimens with no prior exposure. Conversely, specimens with prior carbonation displayed an increased rate of chloride ingress compared to non-carbonated counterparts and a step in the acid soluble chloride content in the region of the carbonation front. The concrete composition appeared to play a role since a greater increase in chloride diffusion coefficient due to prior carbonation was observed in the mix with 50% GGBS replacement than the mix without. These findings suggest that in concrete structures exposed to air and saline environments, the effects of sequential exposure should be characterised.

Mutual Activation Mechanism of Cement–GGBS–Steel Slag Ternary System Excited by Sodium Sulfate

To promote the large-scale recycling of solid waste, the hydration characteristics of blended cement with different amounts of GGBS (ground granulated blast-furnace slag) and SS (steel slag) were investigated. The optimum blending amounts of GGBS and SS in cement were 40% and 10% by mass, and the optimum dosage of Na2SO4 in the C50-S40-SS10 (50 wt.% cement–40 wt.% slag–10 wt.% steel slag) system was 2 wt.%. The flexural and compressive strengths of the C50-S40-SS10 system after adding 2 wt.% Na2SO4 are 57.95% and 9.28% higher than that of pure cement at 28 d. XRD, FT-IR and Ca(OH)2 content analysis were chosen to investigate the hydration products of pure cement and blended cement. The results show that GGBS enhanced the hydration of both cement and SS. And GGBS contributed to the generation of calcium silicoaluminate hydrate (C–A–S–H) in the blended cement system. The addition of Na2SO4 promoted the hydration reaction and contributed to the generation of ettringite (AFt) in the ternary system. The hydration heat evolution results showed that GGBS and SS can reduce the hydration heat of cement. Na2SO4 had similar effects and delayed the time of AFt conversion to monosulfide calcium sulphoaluminate (AFm). A mutual activation mechanism of cement–GGBS–SS ternary system mixed with Na2SO4 was proposed in this study.

Production of ground granulated blast-furnace slag cement: Energy and carbon reduction efficiency of cement-grinding system

Production of ground granulated blast-furnace slag cement: Energy and carbon reduction efficiency of cement-grinding system

Influence of selected mineral additives on properties of recycled aggregate concrete (RAC) considering eco-efficiency coefficients

The paper is focused on the eco-efficiency calculations of recycled aggregate concrete (RAC) consisted of ordinary Portland and blast-furnace slag cements with three fine-grained wastes: quartz powder (Q), limestone powder (L) and fly ash (F). The characteristics of concrete mixes (slump and air content) and hardened concrete properties: 28- and 90-day compressive strength, water absorption as well as the depth of the carbonation (after the accelerated carbonation in the chamber) were examined. In order to parameterize the third feature of contemporary concrete, which is (next to the strength and durability) its sustainability potential, the binder intensity (bi) and carbon intensity (ci) indexes were calculated, taking into account CO2 emissions from cement production and technological processes related to preparation for use of other ingredients. The comparison of the effect of limestone powder and fly ash showed some advantages of the fly ash (taking into account the results of strength tests). However, limestone powder turned out to be more favorable in influencing other properties (especially resistance to carbonation). Nevertheless, the use of fly ash proved to be the most effective in terms of eco-efficiency factors. The pozzolanic properties of F increased the strength of the concrete, reducing both bi and ci values. Furthermore, the presence of F canceled out the negative effect of quartz powder. The use of F together with cement containing ground-granulated blast-furnace slag (GGBS) was most beneficial. Although quartz powder due to technological reasons occurred to be the worst option, its use may be beneficial when CO2 sequestration by concrete carbonation is taken into account. Lower strength and resistance to carbonation of concrete with Q allow CO2 to penetrate deeper into the structure, especially in concrete made of GGBS cement. In this way, the later uptake of CO2 from the atmosphere allows for a partial reduction of the ci value, making RAC more eco-efficient.

A Comprehensive Review on the Ground Granulated Blast Furnace Slag (GGBS) in Concrete Production

In the last few decades, the concrete industry has been massively expanded with the adoption of various kinds of binding materials. As a substitute to cement and in an effort to relieve ecofriendly difficulties linked with cement creation, the utilization of industrial waste as cementitious material can sharply reduce the amount of trash disposed of in lakes and landfills. With respect to the mechanical properties, durability and thermal behavior, ground-granulated blast-furnace slag (GGBS) delineates a rational way to develop sustainable cement and concrete. Apart from environmental benefits, the replacement of cement by GGBS illustrates an adequate way to mitigate the economic impact. Although many researchers concentrate on utilizing GGBS in concrete production, knowledge is scattered, and additional research is needed to better understand relationships among a wide spectrum of key questions and to more accurately determine these preliminary findings. This work aims to shed some light on the scientific literature focusing on the use and effectiveness of GGBS as an alternative to cement. First and foremost, basic information on GGBS manufacturing and its physical, chemical and hydraulic activity and heat of hydration are thoroughly discussed. In a following step, fresh concrete properties, such as flowability and mechanical strength, are examined. Furthermore, the durability of concrete, such as density, permeability, acid resistance, carbonation depth and dry shrinkage, are also reviewed and interpreted. It can be deduced that the chemical structure of GGBS is parallel to that of cement, as it shows the creditability of being partially integrated and overall suggests an alternative to Ordinary Portland Cement (OPC). On the basis of such adjustments, the mechanical strength of concrete with GGBS has shown an increase, to a certain degree; however, the flowability of concrete has been reduced. In addition, the durability of concrete containing GGBS cement is shown to be superior. The optimum percentage of GGBS is an essential aspect of better performance. Previous studies have suggested different optimum percentages of GGBS varying from 10 to 20%, depending on the source of GGBS, concrete mix design and particle size of GGBS. Finally, the review also presents some basic process improvement tips for future generations to use GGBS in concrete.

Improved strength development and frost resistance of Portland cement ground-granulated blast furnace slag binary binder cured at 0 °C with the addition of calcium silicate hydrate seeds

Low ambient temperatures drastically decelerate the strength development of cementitious materials, which shortens the construction season in cold regions. The use of ground-granulated blast furnace slag (GGBFS) in concreting works is usually avoided in winter because of its slower hydration rate relative to Portland cement (PC). In this study, the impacts of calcium silicate hydrate (C-S-H) seeds on the strength development and reaction rate of PC/GGBFS binders cured at 0 °C were investigated. The results showed that the addition of C-S-H seeds can efficiently compensate for the strength loss caused by replacing PC with GGBFS, and this effect is more obvious at a lower GGBFS content (30%) than at a high content (50%). Better frost resistance was gained in the seeded binder containing 30% GGBFS than in the pure PC binder. The enhanced compressive strength and frost resistance in the seeded binary binder were attributed to the accelerated PC reaction rate, enhanced pozzolanic reaction rate and degree of GGBFS, and increased amount of pore-filling hydration products due to the nucleation effect of the C-S-H seeds.

Effects of types and surface areas of activated materials on compressive strength of GGBS cement

This study investigated the effects of changing the type and surface area per unit mass (Sa) of activated materials on the compressive strength of ground granulated blast-furnace slag (GGBS) cement (GGBS > 60%). This study is divided into two parts. The first part involved the selection of activated materials. Compressive strength results show that gypsum improves the early strength of GGBS cement more effectively than does sodium silicate or sodium hydroxide. The gypsum activators increase GGBS activity through sulfates, generating ettringites and C–S–H to increase compressive strength. Chemical analysis shows that the sulfite (SO3) in GGBS cement has more stable compressive strength at 6–8%. The second part of this study investigated the influence of Sa. Gypsum was used as a strength activator. The sulfite in GGBS cement was controlled at 6.5% ± 0.5%, and Sa was adjusted as the variable. Linear regression analysis shows that the change in GGBS cement Sa (Msa) is positively correlated with compressive strength. The value of Msa can be estimated according to the value of Sa and the quantity of ingredients used for the study results (cement, GGBS and gypsum). The compressive strengths of GGBS cement at various curing ages can be predicted using Msa.

Influence of the Type of Cement on the Action of the Admixture Containing Aluminum Powder.

The study of the effect of cement type on the action of an admixture increasing the volume of concrete (containing aluminum powder), used in amounts of 0.5–1.5% of cement mass, was presented. The tests were carried out on cement mortars with Portland (CEM I) and ground granulated blast-furnace slag cement (CEM III). The following tests were carried out for the tested mortars: the air content in fresh mortars, compressive strength, flexural strength, increase in mortar volume, bulk density, pore structure evaluation (by the computer image analysis method) and changes in the concentration of OH− ions during the hydration of used cements. Differences in the action of the tested admixture depending on the cement used were found. To induce the expansion of CEM III mortars, a smaller amount of admixture is required than in the case of CEM I cement. Using the admixture in amounts above 1% of the cement mass causes cracks of mortars with CEM III cement due to slow hydrogen evolution, which occurs after mortar plasticity is lost. The use of an aluminum-containing admixture reduces the strength properties of the cement mortars, the effect being stronger in the case of CEM III cement. The influence of the sample molding time on the admixture action was also found.

Performance of GGBS Cement Concrete under Natural Carbonation and Accelerated Carbonation Exposure

One of the primary problems related to reinforced concrete structures is carbonation of concrete. In many cases, depth of carbonation on reinforced concrete structures is used to evaluate concrete service life. Factors that can substantially affect carbonation resistance of concrete are temperature, relative humidity, cement composition, concentration of external aggressive agents, quality of concrete, and depth of concrete cover. This paper investigates the effect of varying the proportions of blended Portland cement (ordinary Portland cement (OPC) and ground granulated blast-furnace slag (GGBS)) on mechanical and microstructural properties of concrete exposed to two different CO2 exposure conditions. Concrete cubes cast with OPC, and various percentages of GGBS (0%, 30%, 50%, and 70%) were subjected to natural (indoor) and accelerated carbonation exposure. The aim of this paper is to present the research findings and authenticate the literature results of carbonation by using GGBS cement in partial replacement of OPC. The concretes with OPC are compared to concretes with various percentages of GGBS, to assess the carbonation depth as well as rate of carbonation of GGBS-based concretes, under both accelerated carbonation and natural carbonation exposure conditions. Even though GGBS cement increases the carbonation depth, the results are not the same with different GGBS replacement percentages. A correlation is made between concrete samples exposed to 15 ± 2% carbon dioxide (CO2) concentration and those exposed to natural CO2 concentration. The results reveal that the products formed by carbonation are similar under both exposure conditions. The experimental tests also revealed that GGBS cement concrete has a lower carbonation resistance than OPC concrete, due to the consumption of portlandite by the pozzolanic reaction. The combination of 70% OPC and 30% GGBS behaved well enough with respect to accelerated carbonation exposure, the depth of carbonation being roughly equivalent to that of control group (100% OPC). The results also show that rate of carbonation becomes more sensitive as the percentage of GGBS replacement increases (binder ratio), rather than duration of curing. Concretes exposed to natural carbonation (indoor) achieved lower carbonation rates than those exposed to accelerated carbonation.

Effect of the Curing Condition and High-Temperature Exposure on Ground-Granulated Blast-Furnace Slag Cement Concrete

In this study, the effect of curing temperature on the properties of slag cement concrete after high-temperature exposure was studied, and elevated curing temperature (45 ± 2 °C and 95% relative humidity (RH)) was selected to compare with the standard curing temperature (20 ± 2 °C and 95%RH). Four different concrete mixes with the same mix proportion, except for different slag replacement ratios, were used: 0% (reference), 30% (slag), 50% (slag), and 70% (slag). After high-temperature exposure at 200, 400, 600, and 800 °C, the effect of slag replacement, high temperature, and curing temperature on the compressive strength and mineralogical and microstructural properties of slag cement concrete were studied. Test results indicated that the compressive strength of concrete cured for 7 d at elevated temperatures increased by 28.2, 20.7, 28.8, and 14.7% compared with that cured at the standard curing condition at slag percentages of 0, 70, 50, and 30%, respectively. X-ray diffraction (XRD) and Scanning electron microscope (SEM) results revealed that concrete cured at elevated temperatures exhibited a more condensed phase and contained a higher percentage of hydrates than that cured for 7 d in the standard curing condition. However, after 56 d of curing, concrete in the standard curing condition exhibited a more stable phase and a higher concentration of hydrates.

Effects of γ-C2S on the Properties of Ground Granulated Blast-Furnace Slag Mortar in Natural and Accelerated Carbonation Curing

γ-Dicalcium silicate (γ-C2S) is known for its strong carbonation reactivity by which it can capture atmospheric carbon dioxide (CO2), thus, it can be used in construction industries. This paper aims to study the effects of γ-C2S on the properties of ground granulated blast-furnace slag (GGBFS) containing cement mortar and paste in natural and accelerated carbonation curing. The compressive strength of 5% γ-C2S (G5) added to GGBFS cement mortar is higher compared with the control one in natural carbonation (NC) and accelerated carbonation (AC) up to 14 days of curing, but once the curing duration is increased, there is no significant improvement with the compressive strength observed. The compressive strength of AC-cured mortar samples is higher than that of NC. The scanning electron microscopy (SEM) images show that the AC samples exhibited compact, uniform, and regular morphology with less in porosity than the NC samples. X-ray diffraction (XRD) and Fourier transform infra-red (FT-IR) results confirmed the formation of calcium carbonate (calcite: CC) as carbonated products in paste samples, which make the surface dense and a defect-free matrix result in the highest compressive strength. The decomposition of AC samples around 650–750 °C revealed the well-documented and stable crystalline CC peaks, as observed by thermogravimetry analysis (TGA). This study suggests that γ-C2S added to concrete can capture atmospheric CO2 (mostly generated from cement and metallurgy industries), and make the concrete dense and compact, resulting in improved compressive strength.

Comparative Study on Chloride Binding Capacity of Cement-Fly Ash System and Cement-Ground Granulated Blast Furnace Slag System with Diethanol-Isopropanolamine.

Steel bar corrosion caused by chloride was one of the main forms of concrete deterioration. The promotion of chloride binding capacity of cementitious materials would hinder the chloride transport to the surface of steel bar, thereby alleviating the corrosion and mitigating the deterioration. A comparative study on binding capacity of chloride in cement-fly ash system (C-FA) and cement-ground granulated blast furnace slag system (C-GGBS) with diethanol-isopropanolamine (DEIPA) was investigated in this study. Chloride ions was introduced by adding NaCl in paste, and the chloride binding capacity of the paste samples at 7 d and 60 d was examined. The hydration process was discussed via the testing of hydration heat and compressive strength. The hydrates in hardened paste was characterized by X-ray Diffractometry (XRD), Thermo Gravimetric Analysis (TGA), and Scanning Electron Microscope (SEM). The effect of DEIPA on dissolution of aluminate phase and compressive strength was discussed as well. These results showed that DEIPA could facilitate the hydration of C-FA and C-GGBS system, and the promotion effect was higher in C-FA than that in C-GGBS. DEIPA also increased the binding capacity of chloride in C-FA and C-GGBS systems. One reason was the increased chemical binding, because DEIPA facilitated the dissolution of aluminate to benefit the formation of Friedel’s salt. Other reasons were the increased physical binding and migration resistance. By contrast, DEIPA presented greater ability to increase chloride binding capacity in C-FA system, because DEIPA showed stronger ability to expedite the dissolution of aluminate of FA than that of GGBS, which benefited the formation of FS, thereby promoting the chemical binding. Such results would give deep insight into using DEIPA as an additive in cement-based materials.

The curing times effect on the strength of ground granulated blast furnace slag (GGBFS) mortar

This research aims to study the effects of setting times and soundness of the GGBFS cement for various fineness of ground granulated blast furnace slag (GGBFS) as partial replacement ordinary Portland cement (OPC) at 20 wt%, 40 wt% and 50 wt%, on the compressive and flexural strength of GGBFS mortar. A total of 54 test samples and 9 controlled samples of prisms were cast and cured for 7, 28 and 90 days before compressive and flexural strength test. However, the setting times and the soundness test results of GGBFS cement and controlled OPC were investigated. The results showed that GGBFS cement with higher Blaine’s fineness with 40 wt% replacement had the highest compressive strengths of 57.29 MPa and 69.70 MPa at 28 and 90 days of curing duration respectively. Moreover, outperformed OPC with compressive strengths of 55.67 MPa and 61.49 MPa at 28 and 90 days of curing duration, respectively. Setting times decreased with a higher fineness of GGBFS cement, but increased with greater percentages of GGBFS cement, while the average expansion of soundness test is within acceptable limits. Therefore, it can be concluded from this study that curing duration increases the strength of mortar and GGBFS cement is useful for partial replacement of OPC.

The hydration properties of ultra-fine ground granulated blast-furnace slag cement with a low water-to-binder ratio

Based on the fundamental principles of preparing reactive powder concrete (RPC), a new type of RPC was composed by replacing cement with the active powder component ultra-fine ground granulated blast-furnace slag (GGBS). GGBS is proposed as a potential alternative to silica fume (SF), which is currently the most commonly used RPC mineral admixture. In order to improve the brittleness of RPC, a steel fibre with appropriate length/diameter ratio was added. The ultra-fine GGBS (UFS) or SF replacement level was 20% by mass, with a water-to-binder (w/b) ratio of 0.18. The concrete specimens were pre-cured for 6 h at 20 °C and then exposed to steam curing conditions for 3 days. This study investigates the effects of the UFS and the SF on the durability of the RPC by examining the hydration properties, mechanical properties and permeability of RPC. Test results reveal that replacing the cement with UFS or SF does have a significant effect on the hydration properties, our results indicate that the inclusion of SF or UFS can accelerate the early hydration of cement and increase the consumption of Ca(OH)2. The mercury porosimetry and chloride ion penetration tests results revealed that RPC has a very low porosity and very dense structure. RPC with the addition of steel fibre exhibited a higher compressive strength than the RPC without steel fibre. Incorporating UFS into RPC had similar advantages to incorporating SF, but UFS proved to be the more economical admixture.

Effect of Limestone Powder and Fine Gypsum on the Cracking Tendency of Blast-Furnace Slag Cement Concrete Subjected to Accelerated Curing

Thermal stresses are generated in concrete during the accelerated curing process in precast concrete. These stresses may cause concrete to crack, which would have a negative effect on the general concrete performance. This paper provides the results of the thermal stress analysis of concrete containing 25% replacement of ordinary Portland cement (OPC) by ground granulated blast-furnace slag cement (GGBFS) with 3000 cm2/g fineness. A total of 2.5% of limestone powder and 1.75% of fine gypsum by mass of OPC were incorporated in the other concrete mix proportion to check their effect on the cracking tendency of concrete. The concrete was subjected to heat curing. JCMAC, a 3D finite element analysis software developed in Japan, was used in this study for the thermal stress analysis. The heat curing period of one day, similar to generally used in the precast concrete industry for civil engineering products consisting of 3 h preheating period, heating to a peak temperature of 65 °C and this temperature was kept for 3 h, and lastly cooling was used in the study. A standard precast box culvert model member together with some experimental results obtained in the laboratory were used in the analysis. Lower cracking resistance at 1 day was observed in both mix proportions that would lead to cracking at demolding time. Curing sheets were then introduced in the analysis to cover the precast mold during accelerated curing and this showed improvement in cracking resistance of concrete containing limestone powder and fine gypsum.

Sustainable Use of GGBS and RHA as a Partial Replacement of Cement in the Stabilization of Indian Peat

The cement stabilization of peat has been prevalent traditionally throughout the years across the world. However, the drawbacks associated with the manufacturing process of cement finally lead to a great climatic change and environmental threats. Therefore, considering this issue, the present study encourages the use of industrial waste, ground granulated blast furnace slag (GGBS) and agricultural waste, rice husk ash (RHA) as a partial replacement of cement in the stabilization of Indian peat. The collected peats varies with four diverse ranges of organic content (20–76%) comprising three different states in the northeastern province of India. The collected peats were stabilized using cement (5–30%) followed by the determination of optimum cement content based on strength and acidity criteria. The replacement of the cement with GGBS and RHA was done in three different percentages (i.e., 30%, 50%, and 70%) at their optimum cement content. The experimental investigations include compaction, unconfined compressive strength (UCS), pH, electric conductivity (EC), field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The influence of the various proportions of cement–GGBS and cement–RHA mixture, organic content and curing days were addressed precisely. The UCS results reveal that the replacement of cement with GGBS and RHA brings a relatively less strength development as compared to cement alone. However, this study suggests a maximum of 30% cement replacement from their optimum cement content for low organic peat ( 66%) is seen to be more. The pH and EC decreases after the replacement of cement which reduces the ion (Ca2+ and OH−) generation in pore fluid system. FESEM and XRD analyses confirm that the reaction products responsible for strength gain are the same as obtained in cement stabilization. Finally, the replacement of cement with GGBS gives relatively better performance than that of RHA. As GGBS and RHA are an environs threat, thus use of such waste materials can be a well sustainable solution for treating organic soil and peat.

An Experimental Study on Unconfined Compressive Strength of Soft Soil‐Cement Mixtures with or without GGBFS in the Coastal Area of Vietnam

Soft soil is widely distributed in Vietnam, especially in the coastal area. In engineering practice, soft soil cannot be used to build any construction and needs to be improved or treated before building construction. In addition, Vietnam has many pig‐iron or thermal power plants, which annually produce a huge amount of granulated blast furnace slag (GBFS). Thus, the use of this material for soft soil improvement needs to be considered. This paper presents experimental results on the unconfined compressive strength (UCS) of three Vietnam’s soft soils treated with Portland cement and Portland cement with ground granulated blast furnace slag (GGBFS). Binder dosage used in this study is 250, 300, and 350 kg/m3 with the three different water/cement ratios of 0.8, 0.9, and 1.0, respectively. The research results showed that the UCS of soil‐cement mixtures depends on soil type, water/cement ratio, cement type, and binder content. Accordingly, the unconfined compressive strength increased with the increase of binder contents, the decrease of the natural water content of soft soil, water/cement ratios, and clay content. The highest value of UCS of treated soils was found for the soil at Site II with the Portland cement content, cement GGBFS, and water/cement ratio of 873 kg/m3, 2355 kg/m3, and 0.8, respectively. Besides, for all the three soils and two binder types, the water/cement ratio of 0.8 was found to be suitable to reach the highest UCS values of treated soil. The research results also showed that the UCS of treated soil with cement GGBFS was higher than that of treated soil with Portland cement. This indicated the effectiveness of the use of Portland cement with GGBFS in soft soil improvement. There is great potential for reducing the environmental problems regarding the waste materials from pig‐iron plants in Vietnam and the construction cost as well.

Properties of Blast-Furnace Slag Cement Concrete Subjected to Accelerated Curing

Accelerated curing is used for mass production in the precast concrete industry. Autogenous shrinkage and drying shrinkage occur in concrete, during and after accelerated curing. Thus, thermal cracks may occur in concrete due to both heating and cement hydration at early age, whereas drying shrinkage causes cracks after demolding. Ground granulated blast-furnace slag cement (GGBS), a byproduct in steel manufacture, has been used to improve concrete strength development during accelerated curing but poses a challenge of increased shrinkage. In this paper, two types of granulated blast-furnace slag cements were used to study mechanical and shrinkage properties of water cured and concrete subjected to accelerated curing. Limestone powder and gypsums, with two different types of fineness, were other additives used. An accelerated one day curing cycle was adopted that consisted of a 3 h delay period, heating to 65 °C, a peak temperature maintained for 3 h, and, finally, cooling. The results indicated that increment in gypsum fineness increased concrete expansion at one day for both sealed and accelerated cured concrete. In drying condition, similar shrinkage was observed. The addition of gypsum provided slightly lower shrinkage, and this may help to reduce cracking of concrete. Limestone powder improved concrete strength at early age. The difference in blast-furnace cement fineness did not have significant differences in compressive strengths, especially at 28 days.

Influence of alkali activators on the early hydration of cement-based binders under steam curing condition

The effects of water glass, NaOH, Na2SO4, and Na2CO3 on the early hydration of plain cement and two composite binders incorporating 40 mass% ground granulated blast furnace slag (GGBS) and 40 mass% fly ash under the steam curing temperature of 60 °C were investigated. Meanwhile, a 20 °C curing condition was set as a reference. The results showed that water glass, NaOH, and Na2CO3 can improve the exothermic rates of the binders at the acceleration period and promote the reaction of GGBS and fly ash. However, the alkali activators inhibited the hydration of Portland cement at the deceleration period, which was more significant at 60 °C. Thus, the alkali activators cannot efficiently increase the cumulative hydration heat within 16 h under steam curing or even appear to decrease. Na2SO4 shows a better performance than the other three alkalis in the early hydration of the composite binders due to its promotion on the formation of AFt, but it cannot efficiently increase the cumulative hydration heat too. The results also showed that all of the alkali activators significantly decreased the form-removal strength of cement–GGBS composite binder. For cement–fly ash composite binder, the form-removal strengths of the samples activated by a low concentration of water glass and high concentration of Na2SO4 were close to that reacted with water, while the form-removal strengths of the samples activated by other alkaline solutions were lower. Overall, the four alkali activators cannot improve the form-removal strength of steam-cured mortar containing a large volume of mineral admixtures.

경석고 및 황산나트륨을 함유한 하이볼륨 고로슬래그 시멘트의 수화특성

ABSTRACT In order to use the high-volume slag cement as a construction materials, a proper activator which can improve the latent hydraulic reactivity is required. The dissolved aluminum silicon ions from ground granulated blast furnace slag (GGBFS) react with sulfate ions to form ettringite. The proper formation of ettringite can increase the early-age strength of high-volume GGB FS (80%) cement. The aim of this study is to investigate the hydration properties with sulfate activators (sodium sulfate, anhydrite). I n this paper, the effects of Na 2 SO 4 and CaSO 4 on setting, compressive strength, hydration, micro-structure were investigated in high-volume GGBFS cement and compared with those of without activator. Test results indicate that equivalent SO 3 content of 3~5% improve the early-age hydration properties such as compressive strength, heat evolution rate, micro-pore structure in high-volume GGBFS cement. Keywords : high-volume slag cement, hydration, anhydrite, sodium sulfate, early-age strength