Ground Granulated Blast Furnace Slag Binder Research Articles

Experimental study on effective utilization of industrial solid wastes in developing Ultra-High Performance Geopolymer Concrete

<p><a><span style="font-size:12.0pt"><span style="line-height:115%"><span style="font-family:"Times New Roman",serif">This experimental study explores the use of Ground Granulated Blast Furnace Slag(GGBS) and dolomite as alkali activated binders and copper slag as aggregate to achieve a cost-effective and sustainable Ultra-High-Performance Geopolymer Concrete(UHPGC). Several concrete compositions utilizing copper slag as a substitute for natural aggregates were formulated. Tests have shown that the inclusion of 100% copper slag fine aggregate leads to significant improvements in the mechanical properties and density of geopolymer concrete. Specifically, the compressive strength increased by 56.8% and the density increased by 17.5%. To understand the influence of dolomite in GGBS binder, several mixes varying dolomite proportion in GGBS were examined. The compressive strength of the 80% GGBS/20% dolomite geopolymer matrix is 32.8% higher compared to the compressive strength of UHPGC with 100% GGBS. The UHPGC mixture containing 1% crimped steel fibers showed the highest compressive strength, measuring 146.6 MPa. The split tensile and flexural strengths of the 20% dolomite matrix show a significant increase of 30.55% and 30.24% respectively compared to the 100% GGBS matrix. The water absorption and porosity of the 100% GGBS specimen were found to be lower compared to the 20% dolomite UHPGC specimen. The microscopic study reveals the positive impact of dolomite and GGBS on enhancing the bonding of the geopolymer matrix along with decreasing permeability. This study highlights the potential of geopolymer technology in producing ultra-high-performance concrete using GGBS, dolomite, and copper slag.</span></span></span></a></p>

Can Geopolymer Be a Replacement for Portland Cement in Full-Depth Reclamation Projects? Short- and Long-Term Performance Analysis

The fundamental concern of the full-depth reclamation (FDR) technique using Portland cement (FDR-PC) lies in its detrimental effect on the environment. Therefore, researchers are exploring alternative binders that are comparatively greener but compatible with FDR. This study evaluates both the strength and durability aspects of FDR incorporating geopolymer binder (FDR-GP) as an alternative to conventional FDR-PC. Various blends of fly ash (FA) and ground granulated blast furnace slag (GGBS) have been experimented with as geopolymer pre-cursors, ensuring that the additive content does not exceed 20% by weight of the total mix. Sodium hydroxide (NaOH) was utilized for the alkalinization in varying molarities to enhance the performance of the mixes. The experimental design was formulated to achieve a target 7-day unconfined compressive strength (UCS) strength of 4.95 MPa. This was obtained at a lower molarity (M) of 2 M and a 70% FA, 30% GGBS binder content. The mixes performed satisfactorily in both compression and flexure, along with excellent durability properties analyzed through wetting and drying tests. Furthermore, the long-term performance of FDR-GP mixes was investigated with regard to both UCS and flexural strength after 56, 161, and 238 days of curing. Thereafter, a comprehensive microstructural analysis was conducted to understand the fundamental changes in the matrix that influence mix performance. The outcome of this research confirms the potential of using FA/GGBS-based geopolymer as an alternative binder in FDR projects of flexible pavement, the mechanical and durability properties of which adequately satisfy the requirements as stipulated in various design standards.

Improving Soft Subgrade Stability Using a Novel Sustainable Activated Binder Derived from By-Products

Soft soil concerns, due to high compressibility and low bearing capacity, prompted an investigation into stabilizing clay soil. Traditionally, binder including cement or lime has been used as stabilizers though a current requirement of alternatives is stem from environmental concerns. The study focused on the viability of using a novel binary activated blended binder composed of environmentally friendly materials, namely ground granulated blast furnace slag (GGBS) activated by cement kiln dust (CKD). The experimental work included investigating the impact of the developed binders on the Atterberg limits, standard Proctor compaction, California Bearing Ratio (CBR), unconfined compressive strength (UCS), and field-emission scanning electron microscopy (SEM)/energy-dispersive X-ray spectroscopy. CBR tests were conducted after 7 days of curing or soaking, while UCS and SEM analyses were conducted after 7 and 28 days of curing. A fixed binder ratio of 9% was maintained, with GGBS blended at 25%, 50%, and 75% with CKD. For comparison, samples of untreated and treated soils with unary binders from GGBS and CKD were also prepared. Results indicated that activated binders notably decreased soil plasticity and maximum dry density, while elevating optimum moisture content, CBR, and UCS, especially in later stages of treated soil and unary GGBS binder. Unary CKD binder exhibited a similar trend to activated binders. The activating of 25% GGBS with 75% CKD provided the optimum binder which increased the mechanical strengths by about 6 times than untreated soil. SEM revealed substantial formations of C-S-H and C-A-H gel, along with ettringite, intensifying with time. This research provides viable outcomes for stabilizing clay soil using environmentally friendly binders, demonstrating significant improvements in soil properties, particularly when using the binary activated blended binder consisting of GGBS and CKD.Graphical

Effect of activator concentration on setting time, workability and compressive strength of sustainable concrete with alkali-activated slag binder

The global need to reduce carbon dioxide (CO2) emissions prompted studies on sustainable alternatives to conventional concrete made with ordinary Portland cement (OPC) binders. Alkali-activated ground granulated blast furnace slag (GGBS) is a promising sustainable to OPC in terms of the impact on the environment and reduction of CO2 emissions. Concretes and mortars made with alkali-activated binders demonstrate promising fresh and mechanical properties. This article presents the findings of an experimental study investigating the fresh and mechanical properties of mortar using alkali-activated GGBS binder. The activators used were sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) solution with 6 M, 8 M, 10 M, and 12 M molarities. The study assessed their initial setting time, workability, and 28-day compressive strength. The study evaluated the effect of partial replacement of GGBS with 5 % silica fume. The compressive strength was determined after 28 days of curing in three different environments: 1) ambient air temperature, 2) water submersion, and 3) water immersion for 7 days followed by 21 air curing in ambient temperature. The results showed an increase in compressive strength with higher NaOH concentration but a corresponding decrease in initial setting time and flowability. Depending on the curing method, efflorescence, and blue-green pigmentation were seen during the physical assessment of the samples. The highest 28-day compressive strength was 67.5 MPa when the NaOH activator molarity was 10 mol/L which represents an optimum concentration for strength development. Replacing 5 % of the GGBS binder with silica fume resulted in a decrease in the 28-day compressive strength and workability without affecting the initial setting time.

Effect of varying molarity and curing conditions on the mechanical and microstructural characteristics of alkali activated GGBS binder

Geopolymer binder offers a more sustainable choice for producing concrete in comparison to traditional ordinary Portland cement (OPC). The substitution of geopolymer binder for construction practices can decrease carbon dioxide emissions by decreasing OPC usage and repurposing industrial waste materials like ground granulated blast furnace slag (GGBS), fly ash, red mud, silica fume. In order to assess the suitability of GGBS as a binding material, it is essential to conduct conventional tests like consistency, setting times, and compressive strength, which are widely employed in cement testing. This study produced alkali activated paste (AAP) from GGBS and an alkaline activator comprising sodium hydroxide at various molarities from 1 M to 8 M. This investigation focused on the compressive strength of alkali-activated GGBS-based AAP under varying alkali activation molarities and curing conditions, including ambient, hot air oven, and humidity chamber curing. Additionally, the end reaction products of AAP showing higher compressive strength were examined for scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), x-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analysis. The experimental outcomes indicated that GGBS reduced the final setting time of AAP while increasing its compressive strength. Additionally, increasing the quantity of NaOH in the AAP increased its compressive strength. Furthermore, the research findings indicated that the mechanical properties of the alkali-activated GGBS-based material were notably influenced by the chosen curing conditions. Specifically, ambient curing demonstrated superior compressive strength, measuring at 47.06 MPa after 28 days, surpassing the results obtained from hot air oven curing and humidity curing.

Preparation and characterization of mortar specimens based on municipal solid waste incineration fly ash-activated slag

Municipal solid waste incineration fly ash (MSWIFA) contains a large amount of heavy metals, inhibiting resource utilization. This study used MSWIFA as an alkali activator and ground-granulated blast-furnace slag (GGBS) as a precursor to prepare the MSWIFA GGBS binder. Based on this, used the iron tailing sand instead of natural river sand as fine aggregate prepared mortar specimens by cooperative compression molding. Compressive strength, bulk density, water absorption, and heavy metal leaching tests were conducted and combined with micro XRD, FTIR, and SEM examinations to characterize the mortar specimens. The results show that the optimal MSWIFA: GGBS was 2:8. It was also found that increasing the molding pressure was beneficial to strength development. Compared to the specimens without the application of molding pressure, the 3 d and 28 d strength values increased by 148.6 and 122.2%, respectively, after the application of 35 MPa molding pressure. The reason is that the pressure effect can increase the cohesion of the particles, promote the hydration reaction to proceed, and the hydration products increase to fill the pores, increase the structural compactness and promote strength development. The resource utilization of MSWIFA must be guaranteed not to produce environmental pollution simultaneously. For this reason, the heavy metal leaching test was conducted on 28 d mortar specimens, and the results showed that the leaching rates of Zn, Pb, Cu, Cr, and Ni met the requirements of the Chinese Standard (GB16889-2008). The research results can provide a theoretical basis for the large-scale recycling of MSWIFA.

Engineering performance and microstructure characteristics of natural marine sediment stabilized with quicklime-activated GGBS under different lime proportions

The safe treatment of marine sediment has been a global-scale challenge. To reduce the environmental impacts associated with Portland cement (PC), an environment-friendly binder consisting of quicklime and ground granulated blast-furnace slag (GGBS) was used in the stabilization/solidification of natural marine sediment. Although the combination of lime and GGBS is used to stabilize the sediment with very low water content or moderate water content in previous studies, the natural marine sediment with such a high water content has not been treated by the quicklime–GGBS binder up to now. Therefore, a series of tests were performed to study the physicochemical, mechanical, and microstructural characteristics of quicklime–GGBS stabilized sediments. The results indicated that the quicklime–GGBS solidified/stabilized sediment had a similarly low water content at a proper quicklime-binder ratio to that of PC-stabilized sediments. The pH of quicklime–GGBS solidified sediments gradually decreased as the quicklime-binder ratio decreased and the curing period increased. The unconfined compressive strength (UCS) of quicklime–GGBS stabilized sediments was 1.4 times higher than that of the corresponding PC-stabilized sediments using the same test conditions. The hydration products effectively bonded the sediment particles and filled the pores between the sediment particles, facilitating the improvement of the UCS of the quicklime–GGBS stabilized sediment. The findings indicated that the use of GGBS and a small amount of quicklime can replace PC to stabilize natural marine sediment with high water content. This would be to provide binder dosage and component proportion for the field application of quicklime–GGBS binder and to significantly improve the economical and environmental effects of the treatment of high water content sediment. HIGHLIGHTS Innovative lime-activated GGBS is used as a binder in the improvement of sediment with ultrahigh water content. The water content, pH, and UCS of lime–GGBS stabilized sediments are contrastively studied. The engineering performances of lime-GGBS stabilized sediments are better than those of PC-stabilized sediment. An optimal and appropriate lime-binder ratio is suggested. Microstructure mechanism of lime–GGBS stabilized sediment is revealed through series of micro-tests.

Alternative cleaner production of sustainable concrete from waste foundry sand and slag

The objective of this study was to synthesize a sustainable concrete material from readily available waste and by-products; Ground Granulated blast furnace slag (GGBFS) and waste foundry sand (WFS). GGBFS was alkali-activated using NaOH solution and used as a binder to completely replace Ordinary Portland cement (OPC). Concurrently, WFS was used as fine aggregate to replace natural sand in concrete production. An optimization experimental program of various conditions was used to get the best concrete specimens in terms of high strength and low metal leachability. The GGBFS, WFS, and crushed stones mix design formulations used were; 20:40:40, 25:37.5:37.5, 30:35:35, and 40:30:30 respectively. The specimens were cured for 7, 14, 28, 56, and 90 days, respectively. The liquid to solid (L/S) ratio was varied from 15% to 30%. The concrete specimens' with a mix design formulation; 40% GGBFS binder, 30% WFS, and 30% crushed stones with 15% L/S ratio cured for 90 days yielded the highest Unconfined Compressive Strength (UCS) of 12.7 MPa. The best concrete specimen was evaluated for durability, structural performance, and long-term metal leachability. The XRD results showed that hydration products (CSH) play a crucial role in the strength development of the concrete. The metal leachability and durability results show that the metals were successfully immobilized in the concrete specimens with acceptable durability properties. Thus, the synthesized concrete specimens can be used for loadbearing concrete masonry units as per ASTM C90 and other building and construction applications as per ASTM C34- 03, ASTM C62-10. Furthermore, the study demonstrated that a sole alkaline activated GGBFS can completely replace OPC and concurrently use WFS as fine aggregate to replace natural sand in concrete production. As a result, the reutilization rate of WFS can be increased from 20% to 30%.

Effect of accelerators on Ca(OH)2 activated ground granulated blast-furnace slag at low curing temperature

The early effects of three accelerators on a Ca(OH)2 activated ground granulated blast-furnace slag binder at low curing temperatures are discussed. The compressive strength, hydration kinetics, hydration products, and microstructures were investigated by isothermal calorimetry, X-ray diffraction, mercury intrusion porosimetry, scanning electron microscopy, and nuclear magnetic resonance. Results show that accelerators continue to promote the strength development of pastes in the early stage during low-temperature curing, especially with sodium sulfate, which exhibits a higher strength and hydration degree in the early stage. However, accelerators cannot effectively improve the pore structure at low-temperature curing, which severely restricts the development of strength, compared with that at 20 °C. Furthermore, a good correlation was found between the initial strength development and the limit equivalent ionic conductivity (LEIC), suggesting that LEIC influences the reaction acceleration of blast-furnace slag at an early age.

Immobilization of molybdenum by alternative cementitious binders and synthetic C-S-H: An experimental and numerical study

Excavation operations during construction produce millions of tons of soil sometimes with high leachable molybdenum (Mo) contents, that can lead to risks for both human health and the environment. It is therefore necessary to immobilize the Mo in excavated soils to reduce pollution and lower the costs of soil disposal. This paper studies the immobilization of Mo by three cementitious binders. To this end, one Ordinary Portland cement (OPC), one binder composed of 90% ground granulated blast furnace slag (GGBS) and 10% OPC, and one supersulfated GGBS binder were spiked with sodium molybdate at six different Mo concentrations from 0.005 wt% to 10 wt% before curing. In addition, to gain mechanistic insights, the capacity of synthetic calcium silicate hydrates (C-S-H) to immobilize Mo was studied. This study was completed by thermodynamic modeling to predict the immobilization of Mo at low Mo concentrations (<0.005 wt%). Paste leaching tests results showed that more than 74% of the initial Mo spike was immobilized by the three binders. The supersulfated GGBS binder consistently showed the highest retention levels (92.0 to 99.7%). The precipitation of powellite (CaMoO4) was the dominant mechanism of Mo retention in all binders and most leaching solutions were oversaturated with respect to powellite. Also, in C-S-H syntheses, Mo was largely immobilized (>95%) by the coprecipitation of powellite. Thermodynamic modeling was in good agreement with measured values when the equilibrium constant of powellite was modified to LogK = −7.2. This suggested that powellite is less stable in cementitious environments than would be expected from thermodynamic databases. Moreover, modeling showed that, for a solution at equilibrium with portlandite or C-S-H, the Mo concentration is limited to 1.7 mg/L by powellite precipitation. In contrast, for a solution saturated with respect to ettringite, the threshold concentration for powellite precipitation is 6.5 mg/L.

The role of recycled waste glass incorporation on the carbonation behaviour of sodium carbonate activated slag mortar

This study investigates the influences of recycled waste glass powder (RGP) on the carbonation behaviour of sodium carbonate activated ground granulated blast furnace slag (GGBS) mortars. The effect of activator dosages, types and RGP addition on resistance to carbonation are evaluated. The results indicate a high dosage of sodium carbonate or water glass combination as activator always can enhance the ability of resistance to carbonation. Furthermore, the addition of 30% RGP in the GGBS binder system seems to significantly improve the resistance to carbonation of mortars. The carbonation shrinkage is reduced after RGP incorporation; at the same time, a higher strength performance is observed. The RGP in sodium carbonate activated GGBS blends shows no influence on the species of reaction products. However, after carbonation, the sample containing RGP promotes the formation of nahcolite, while less bound water loss and calcium carbonate formation are identified. A high volume of gel pores (<10 nm) is formed in the RGP sample compared to specimens only containing GGBS. These properties contribute to a better resistance to carbonation for RGP containing sodium carbonate activated GGBS mortars.

Use of Coal Bottom Ash and CaO-CaCl2-Activated GGBFS Binder in the Manufacturing of Artificial Fine Aggregates through Cold-Bonded Pelletization.

This study investigated the use of coal bottom ash (bottom ash) and CaO-CaCl2-activated ground granulated blast furnace slag (GGBFS) binder in the manufacturing of artificial fine aggregates using cold-bonded pelletization. Mixture samples were prepared with varying added contents of bottom ash of varying added contents of bottom ash relative to the weight of the cementless binder (= GGBFS + quicklime (CaO) + calcium chloride (CaCl2)). In the system, the added bottom ash was not simply an inert filler but was dissolved at an early stage. As the ionic concentrations of Ca and Si increased due to dissolved bottom ash, calcium silicate hydrate (C-S-H) formed both earlier and at higher levels, which increased the strength of the earlier stages. However, the added bottom ash did not affect the total quantities of main reaction products, C-S-H and hydrocalumite, in later phases (e.g., 28 days), but simply accelerated the binder reaction until it had occurred for 14 days. After considering both the mechanical strength and the pelletizing formability of all the mixtures, the proportion with 40 relative weight of bottom ash was selected for the manufacturing of pilot samples of aggregates. The produced fine aggregates had a water absorption rate of 9.83% and demonstrated a much smaller amount of heavy metal leaching than the raw bottom ash.

Prevention of potential strength degradation due to conversion of C2AH8 formed in CaO-Ca(HCOO)2-activated GGBFS binder using CaSO4

Recently, the combined use of calcium oxide (CaO) and calcium formate (Ca(HCOO)2) has been proposed as an alternative activator for ground granulated blast furnace slag (GGBFS) (referred to as CaO-Ca(HCOO)2-activated GGBFS system). However, this clinker-free binder system produces calcium aluminate hydrate (C2AH8), generally leading to the degradation of cementitious binder systems by its conversion to other phases. Thus, in this study, attempts to remove C2AH8 from this system without losing the strength are suggested by the use of two additives (i.e., calcium sulfate (CaSO4) and calcium nitrate (Ca(NO3)2), respectively). Results revealed that the above-mentioned additives completely remove C2AH8 in the initial curing stage via its conversion to ettringite or NO3- and NO2-AFm, respectively. In addition, the additives reduced the extent of the total shrinkage and the standard deviation of strength results of triplicate samples. However, CaSO4 exerted a beneficial effect on the strength, while Ca(NO3)2 exerted a marginal or detrimental effect on the strength. Therefore, this study suggested a new mixture form of an activator, comprising CaO, Ca(HCOO)2, and CaSO4, to activate GGBFS for maintaining strength without the conversion issue of C2AH8.

The mechanical strength and durability properties of ternary blended cementitious composites containing granite quarry dust (GQD) as natural sand replacement

Cementitious composites are the most used man-made materials in the world with a global annual production quantum of 25 billion tonnes worldwide, contributing approximately 5% to the global greenhouse gas emissions. In the initiative to reduce the carbon footprint of cementitious composite production, are growing interests in the large volume reuse of industrial by products such as ground granulated blast-furnace slag (GGBS), pulverized fuel ash (PFA) and granite quarry dust (GQD) in cementitious composites production. Such an approach offers a two-fold solution towards addressing the waste management problem related to those industry by-products. At the same time however; reduction of carbon footprints of cementitious composite materials exists. However, in order to enable scalable applications of such a recycling approach, a comprehensive body of knowledge on the mechanical strength and durability performance of the cementitious composite products containing a large volume of the materials needs to be established. Hence, it is the primary aim of the study to report a comprehensive assessment on the mechanical strength and durability properties of high strength cementitious composites. These materials are produced with a large volume of the aforementioned materials as the primary binder and aggregate phase. Throughout the investigation, high strength cementitious composites mixes were produced with a large volume of PFA and GGBS binder. Then phase coupled with ordinary Portland cement (OPC). GQD was used as the fine aggregate phase in substitution of natural river sand at various level of substitution ranging between 0 and 100% by volume. The cementitious composites were characterized in terms of its fresh cementitious composites. Its flowability and hardened cementitious composites properties mainly bulk density, compressive strength, flexural strength, and Ultrasonic Pulse Velocity were also assessed. In addition, the durability properties such as water absorptivity and porosity were also covered in this experimental program. Pore continuity was assessed in terms of air permeability and capillary absorption of the hardened specimens according to the testing age. This paper has also covered the dimensional stability assessment in terms of drying shrinkage. Besides, a comprehensive microstructural assessment was also performed to examine the microstructure morphology. From the results, we found full incorporation of GQD as NRS without significant impairment to the mechanical, durability and length change performance. Thus, the production of sustainable high strength cementitious composites with large volume recycling of GQD is feasible which in turn reduces the depletion on the natural river sand resources.

Optimization of lightweight GGBFS and FA geopolymer mortars by response surface method

In the first stage of the paper, the effect of binder content, curing temperature and curing time on the compressive strength of light-weight geopolymer mortar (LWGM) was investigated. The base materials used for LWGM are ground granulated blast furnace slag (GGBFS) and fly ash (FA). The main components of LWGM are lightweight pumice aggregate and alkali activated FA or GGBFS binder. Effectiveness of aforementioned parameters was examined in terms of variation of the compressive strengths of LWGMs. The experiments were performed on LWGM cubes under curing temperatures of 60, 80, 100 and 120°C with curing period of 2, 6, 8, 24, 48 and 72h. The alkaline activator is a mix of 12M NaOH solution with sodium silicate in ratio of 1:2.5. The ratio of alkaline solution to binder was taken as 0.50. 7 binder contents were taken between 650 to 1250kg/m3 with 100kg/m3 increment. Full factorial experimental program was adopted to observe compressive strength development of LWGMs. Therefore, 336 data samples were obtained. The second stage of the paper is to optimize those experimental parameters through response surface method. Test results indicate that the increment in the binder content increases the compressive strength of LWGM. The strength increases with the increase of curing temperature and curing period of LWGM. The experimental verification indicated a good agreement with optimized results.

Contributions of fly ash and ground granulated blast-furnace slag to the early hydration heat of composite binder at different curing temperatures

Hydration heat evolutions and non-evaporable water contents of binders and reaction degrees of fly ash and ground granulated blast-furnace slag (GGBS) were tested to investigate the contributions of fly ash and GGBS to the early hydration heat of composite binders at 25°C and 50°C. Results show that fly ash makes a very small contribution to the early hydration heat of composite binder at 25°C, but GGBS makes a considerable contribution at 25°C. Elevated temperature enhances the contributions of both fly ash and GGBS to the early hydration heat of composite binder significantly. The promoting effect of elevated temperature on the hydration heat and non-evaporable water content of GGBS binder is greater than that of fly ash binder. The reaction heat per unit mass of GGBS is only 16·7% higher than that of fly ash. The main reason for the difference of hydration heats between GGBS binder and fly ash binder is that GGBS shows much higher hydraulic activity than fly ash.

알칼리 활성화 슬래그 시멘트의 특성에 미치는 Al2O3의 영향

This research investigates the influence of ground granulated blast furnace slag (GGBFS) composition on the alkali-activated slag cement (AASC). Aluminum oxide (Al2O3) was added to GGBFS binder between 2% and 16% by weight. The alkaline activators KOH (potassium hydroxide) was used and the water to binder ratio of 0.50. The strength development results indicate that increasing the amount of Al2O3 enhanced hydration. The 2M KOH + 16% Al2O3 and 4M KOH + 16% Al2O3 specimens had the highest strength, with an average of 30.8 MPa and 45.2 MPa, after curing for 28days. The strength at 28days of 2M KOH + 16% Al2O3 was 46% higher than that of 2M KOH (without Al2O3). Also, the strength at 28days of 4M KOH + 16% Al2O3 was 44% higher than that of 4M KOH (without Al2O3). Increase the Al2O3 contents of the binder results in the strength development at all curing ages. The incorporation of AASC tended to increases the ultrasonic pulse velocity (UPV) due to the similar effects of strength, but increasing the amount of Al2O3 adversely decreases the water absorption and porosity. Higher addition of Al2O3 in the specimens increases the Al/Ca and Al/Si in the hydrated products. SEM and EDX analyses show that the formation of much denser microstructures with Al2O3 addition.

Assessment of CO2 reduction of alkali-activated concrete

Although alkali-activated (AA) concrete is generally regarded as one of the most effective concrete technologies for reducing CO2 emissions, very few investigations have been carried out on the assessment of the CO2 reduction of such concrete. The present paper reports an evaluation procedure for the CO2 reduction of AA concrete. The studied system considers all of the steps from the cradle to pre-construction. CO2 reduction for secondary precast concrete products is also evaluated with reference to practical examples wherein ground granulated blast-furnace slag (GGBS) cement is replaced with AA GGBS binder. Comparisons of the performance efficiency indicators, binder and CO2 intensities, reveal that the contribution of the binder to the total CO2 emission is more significant in ordinary Portland cement (OPC)-based concrete than in AA concrete, whereas the contribution of aggregate transportation becomes more critical in AA concrete than in OPC-based concrete. The reduction rate of CO2 emission of AA concrete relative to OPC concrete commonly ranges between 55 and 75%. In addition, the CO2 reduction rate in secondary precast concrete products that use AA GGBS binder instead of GGBS cement can be evaluated as approximately 20% when the total aggregate-to-binder ratio ranges between 3.0 and 4.0. On the other hand, Ca(OH)2-based AA GGBS concrete shows a CO2 intensity that is approximately 2.4 times lower than that of OPC concrete. Overall, the slope of the increasing rate of the CO2 intensity against the binder intensity is lower in Ca(OH)2-based AA GGBS concrete than in OPC-based concrete.

The influence of high-temperature curing on the hydration characteristics of a cement–GGBS binder

The influence of high temperature curing at early ages on the hydration characteristics of a complex binder containing ground granulated blast furnace slag (GGBS) was investigated. High-temperature curing at early ages promotes the early hydration of cement, but it hinders the later hydration, and leads to large pores in the microstructure. So the long-term strength of cement mortar cured under high temperature at early ages is lower than that cured at under 20°C. The hydration of a cement–GGBS complex binder is more sensitive to temperature than is cement, and the strength gain rate of a cement–GGBS mortar is higher than that of cement mortar under high temperature curing at early ages. After high temperature curing at early ages, the later hydration of the cement fraction of the complex binder is hindered, but the later reaction of GGBS fraction is not influenced. The further reaction of GGBS increases the C–S–H gel quantity and improves the pore structure. Therefore, the cement–GGBS mortar gains a high early strength under high temperature curing at early ages, and its strength has a considerable increment at later ages due to the contribution of the reaction of GGBS.

Use of red gypsum in soil mixing engineering applications

This paper describes a laboratory trial to test the effectiveness of a waste-based binder as a cement replacement for deep in situ soil stabilisation. The binder is composed of red gypsum, a co-product of the production of white pigment titanium dioxide, and ground granulated blast furnace slag (GGBS), with a small addition of lime to increase soil pH and enable pozzolanic reactions to occur. The waste binder was mixed with a number of typical UK soils and cured for 7, 14, 28, 56 and 112 days in wet and dry conditions. Samples were then tested for undrained shear strength and stiffness, and results compared with values exhibited by soils mixed with Portland cement. Selected samples were also subjected to X-ray diffraction analysis. Results showed that, while not achieving strengths as high or hardening as rapid as samples mixed with Portland cement, samples mixed with the gypsum–GGBS binder achieved high strengths and stiffness, and demonstrated that gypsum–GGBS binders have the potential to be used as cement replacements in ground improvement.