Addition Of Ground Granulated Blast Furnace Slag Research Articles

Phase evolution and microstructure changes induced by accelerated carbonation in natural hydraulic lime paste with GGBFS addition

Carbonation is a primary factor driving the continuous improvement of the long-term performance of natural hydraulic lime (NHL). This research systematically examines the impact of accelerated carbonation (3 % CO2) on the carbonation depth, phase composition, microstructure, and compressive strength of hardened natural hydraulic lime (NHL) pastes mixed with different amounts of ground granulated blast furnace slag (GGBFS), termed as S-NHL. The findings show that the hydration reaction products of GGBFS and Ca(OH)2 (CH), such as C3AH10, C4AĈH11, and C-S-H, densify the microstructure of S-NHL, resulting in a decrease in carbonation depth with increasing GGBFS content. Accelerated carbonation (AC) promotes the rapid transformation of a significant quantity of CH into calcite in S-NHL, with the carbonation of CH occurring more readily than the carbonation of hydration reaction products. Throughout the AC process, NHL contains only calcite-type calcium carbonate. In contrast, after 28 days of AC, the carbonation of hydration reaction products such as C3AH10 and C-S-H in S-NHL produces a minor amount of aragonite and vaterite. AC continuously reduces the total pore volume and porosity of S-NHL, but the average pore diameter and most probable pore diameter initially decrease and then slightly increase. AC significantly reduces the large pores in S-NHL, ultimately resulting in pores predominantly composed of capillary pores (50–1000 nm). AC facilitates the development of compressive strength in S-NHL paste, with the increase in compressive strength being positively correlated with its CH content.

Experimental Study on Performance and Mechanism of High-Strength Artificial Blocks Based on Dredged Silt

This paper investigates the preparation and properties of high-strength artificial blocks made from dredged silt with a clay content of 52.0%. A comparative analysis of the mechanical properties of dredged silt blocks produced using semi-dry pressing and vibration molding methods was conducted. The study examined the effects of using fly ash (FA) and ground granulated blast-furnace slag (GGBS) as substitutes for cement on the compressive strength, splitting tensile strength, and dry shrinkage of the blocks. Additionally, the microstructure of the dredged silt blocks was analyzed using scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and thermogravimetric analysis. The results show that specimens prepared using the pressing method exhibit better mechanical performance with compressive and splitting tensile strength reaching 64.8 MPa and 5.6 MPa at 28 d, respectively, which increased by 111.07% and 143.48% compared to specimens prepared through vibration molding. The addition of FA and GGBS reduces the early strength of the block to a certain extent but without a significant adverse effect on later strength. GGBS demonstrates faster hydration and a better filling effect. The addition of GGBS or FA refines the pore structure and reduces the diameter of pores in the paste, which is beneficial for improving the dry shrinkage performance of the block. At 120 d, the dry shrinkage of blocks containing 50% FA and GGBS shows a reduction of 29.7% and 27.1%, respectively, compared to blocks made with cement. The properties of the silt blocks can be notably enhanced through mechanical force, particle gradation, and hydration action. The preparation of artificial blocks such as road bricks and ballast blocks using dredged soil as the main raw material has been applied in projects such as the Yangtze River waterway regulation in China and Skikda Port in Algeria.

Optimisation of mechanical properties and pore structure of lightweight geopolymer concrete

Lightweight geopolymer has good physical and mechanical properties, thermal and chemical stability and low carbon dioxide emissions. The development of high-strength lightweight geopolymer concrete (LGC) for load-bearing structures can expand geopolymer applications. The use of ground granulated blast-furnace slag (GGBFS) to improve the mechanical properties and pore structure of LGC was investigated. The ultimate compressive stress of LGC containing GGBFS were analysed, as well as the variation in microscopic pore structure. Specimens of LGCs with different strengths (LC20, LC30 and LC40) were investigated. As the GGBFS content increases, the ultimate compressive stress and specific strength of LGC increases, while the strain corresponding to the peak stress decreases, indicating that the mechanical properties and deformation resistance of LGC are improved. The carbon dioxide emissions of LGC are less than those of cement-based lightweight concrete, indicating that LGC has good sustainability. Moreover, the addition of GGBFS can produce more gel and reduce the volume proportion of capillary pores and air pores, resulting in LGC densification. Recommended GGBFS contents for strength grades LC20, LC30 and LC40 are 0–12.7%, 12.7–24.6% and 24.6–30%, respectively. The LGC is lightweight and has high strength, and has potential for application in civil engineering.

Influence of combined substitution of slag and fly ash in improving the pore structure and corrosion resistance of foam concrete mixtures used for reinforced concrete applications

Foam concretes (FCs) have been used for several light-weight applications demanding low strength; however, their use for reinforced concrete (RC) applications is limited since high macrovoid amounts result in weaker matrices. The high w/c and overlapping of macrovoids have been identified as critical factors constituting a permeable microstructure in FC systems. Since corrosion performance is a critical aspect in the design of RC members and that the durability parameters of concrete, such as its porosity, pore size distribution, and permeability, also play a vital role in restricting the diffusion of chloride ions, particularly in the cover region of members, it is imperative to determine these properties and thoroughly understand the material behaviour or characteristics. In the current study, five FC mixtures (GF0 to GF4) were produced using ground granulated blast furnace slag (GGBS) and fly ash (FA) as a replacements for cement and sand, respectively, at different dosages, considering both economic and environmental aspects. The principal objective of the study is to determine the pore and permeability related properties of produced FCs, assess their corrosion performance, and ascertain their suitability for RC applications by comparing their performance with that of conventional M25-grade concrete. Also, the influence of the combined effect of GGBS and FA addition and the individual effect of FA addition were assessed. The research findings showed that FCs had a higher water absorption capacity and porosity compared to M25 concrete. In addition, the inclusion of GGBS and FA resulted in a decrease in water absorption by 8%–19% and a decrease in porosity by 23%–36% compared to the control FC mixture. The Mercury Intrusion Porosimetry (MIP) results indicated a substantial enhancement in gel pores, threshold, and critical pore diameter, while the size of the larger capillary pore decreased by 90%–95% when GGBS and FA were added compared to the control FC mixture. The scanning electron microscopy (SEM) analysis and binary images from the image analysis revealed the presence of uniformly distributed and distinct macrovoids formed by foam. These macrovoids were predominantly found within the size range of 7.1μm – 100 µm. The addition of GGBS and FA particles to FC mixes resulted in a significant improvement in the chloride ion permeation (CIP) class, reducing it from 'High' to 'Very Low' compared to M25 concrete. The Accelerated Corrosion Test (ACT) results obtained from FCs demonstrated a significant increase in cracking time ranging from 30% to 323%, as well as a notable decrease in mass loss ranging from 56% to 85% when compared to M25 concrete. The Fourier transform infrared (FTIR) and energy dispersive spectroscopy (EDS) analysis results revealed the presence of corrosion products, including feroxyhyte, akageneite, and Friedel's salt crystal, in both FCs and M25 concrete, indicating the occurrence of corrosion by the chloride ions present in the NaCl solution outside the specimen. Overall, the porosity, CIP, and corrosion resistance of FC with GGBS and FA are superior to those of the M25 concrete, making it suitable for use in RC applications.

Mechanical, durability and microstructural characterization of cost-effective polyethylene fiber-reinforced geopolymer concrete

Portland cement is widely used in the construction industry. Its production contributes to carbon dioxide emissions, urging the need for sustainable alternatives. The present study aims to evaluate the strength, durability, microstructural properties, and cost-effectivity of geopolymer (GP) concrete containing polyethylene (PE) fibers, with fly ash (FA), ground-granulated blast furnace slag (GGBFS), and calcium magnesium carbonate (CaMg(CO3)2 known as dolomite) as binders. PE fiber used has an ultra-high molecular weight. Six different mixtures were produced with FA, GGBFS, dolomite, and/or PE fiber. The control mix used only FA as a binder without PE fiber. Fresh and mechanical properties, including slump value, compressive strength, and split tensile strength, were determined, and non-destructive tests, such as electrical resistivity and ultrasonic pulse velocity, were conducted. The durability of GP was evaluated through initial surface absorption and capillary suction absorption tests at different curing ages. Microstructural and mineralogical characteristics were analyzed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). The results revealed that the addition of PE fibers and CaMg(CO3)2 reduced the workability of GP by 30.22% in comparison with that of PE fiber along with GGBFS. Compared to the reference mix at 28 days, incorporating 20% GGBFS resulted in the highest improvement of 76.89% and 104.86% in compressive and split tensile strength, respectively. GP sample with 20% GGBFS replacement of FA presented the highest reduction of 44.4–41.63% for initial and secondary rate of absorption. SEM analysis showed that the addition of GGBFS and CaMg(CO3)2 to fiber-reinforced FA-based geopolymer mixes developed a denser and more homogenous matrix with improved mechanical behavior due to the co-existence of C−S−H and aluminosilicate gel. PE fibers improve the toughness properties by helping to absorb energy and bridging cracks. The development of a stronger matrix was characterized by C−S−H, calcium aluminate oxide (carbonate) hydroxide (C4AHx) and quartz. A one-way ANOVA analysis and cost analysis demonstrate the cost-effectiveness of partially replacing FA with CaMg(CO3)2 and GGBFS in PE fiber-reinforced GP concrete.

Effect of the elevated temperature on the mechanical properties of geopolymer concrete using fly ash and ground granulated blast slag

PurposeTo investigate the mechanical properties of geopolymer concrete at elevated temperatures.Design/methodology/approachThe investigation involved studying the influence of partially replacing fly ash with ground granulated blast furnace slag (GGBS) at different proportions (5%, 10%, 15%, 20% and 25%) on the composition of the geopolymer. This approach aimed to examine how the addition of GGBS impacts the properties of the geopolymer material. The chemical NaOH was purchased from the local supplier of Jamshedpur. The alkali solution was prepared with a concentration of 12 M NaOH to produce the concrete. After several trials, the alkaline-to-binder ratio was determined to be 0.43.FindingsThe compressive strength values at 28 days for specimens FG1, FG2, FG3, FG4 and FG5 are 35.42 MPa, 41.26 MPa, 44.79 MPa, 50.51 MPa and 46.33 MPa, respectively. The flexural strength values at 28 days for specimens FG1, FG2, FG3, FG4 and FG5 are 5.31 MPa, 5.64 MPa, 6.12 MPa, 7.15 MPa and 6.48 MPa, respectively. The split tensile strength values at 28 days for specimens FG1, FG2, FG3, FG4 and FG5 are 2.82 MPa, 2.95 MPa, 3.14 MPa, 3.52 MPa and 3.31 MPa, respectively.Originality/valueThis approach allows for the examination of how the addition of GGBS affects the properties of the geopolymer material. Four different temperature levels were chosen for analysis: 100 °C, 300 °C, 500 °C and 700 °C. By subjecting the geopolymer samples to these elevated temperatures, the study aimed to observe any changes in their mechanical.

4-year monitoring of degradation mechanisms of seawater sea-sand concrete exposed to tidal conditions: development of chemical composition and micro-performance

In tidal zones, the transfer of conductive ions accelerates concrete deterioration due to dry-wet cycles, temperature, and humidity gradients over time. Thus, this study investigates the effects of ground granulated blast furnace slag (GGBS), silica fume (SF), and metakaolin (MK) on the deterioration rate of seawater Sea-sand concrete (SWSSC) exposed to tidal conditions for four years caused by carbonation, sulphate and chloride penetration. Results showed continuous exposure to MgSO4, reduced Fe content and converted AFm into AFt, contributing to an increase in total SWSSC porosity of 12.9% while reduced to 10.2%, 7.4% and 7.3% with the optimal addition of GGBS, SF and MK. In combined sulphate and chloride-rich conditions, enhanced gel phase physical properties were more influential than AFm phases in increasing chloride binding capacity. SF suppressed AFt expansion, formed dense C−S−H with optimal Ca/Si ratio and physically increased the chloride binding capacity of SWSSC. Similarly, despite its high alumina content, MK restricted chloride mobility mainly through C−S−H and, subsequently, AFm phases. Additionally, through its initial acceleration of calcium-hydroxide consumption, SF reduced alkalinity and minimized the formation of CaCO3, outperforming MK in mitigating carbonation. Higher CaO and MgO in GGBS-mixed samples led to dolomite formation in severely carbonated zones, causing long-term mechanical strength reduction. In summary, SF significantly enhanced SWSSC durability and served as an effective additive in tidal-exposed SWSSC.

Early performance and bonding mechanism of metakaolin (MK)- ground granulated blast furnace slag (GGBS) based geopolymer road repair mortar

ABSTRACT Metakaolin (MK) and ground granulated blast furnace slag (GGBS) based geopolymers have been utilised as materials for concrete road repair. However, their early-stage performance and bonding mechanism as rapid repairs are not well understood. This research investigated the workability, early strength development and bonding mechanism of geopolymer repair mortars with different GGBS contents. The reaction kinetics and reaction products of the geopolymer repairs were analyzed through reaction heat evolution and FTIR, and the microstructure of the bonding interface was examined using BSE-EDS. Results showed that geopolymer repair mortars with higher GGBS content exhibited shorter setting times, higher flowability, and higher compressive strength. Geopolymers demonstrated a one-dimensional rod-shaped nucleation pattern during hardening, and the crystallization rate decreased with GGBS addition. GGBS increased the formation of C-A-S-H gels and accelerated the geopolymerization process. However, excessive GGBS reduced bond strength due to the introduction of microcracks. A GGBS content of 60 wt.% is recommended in this investigation. The study also revealed that the cement substrate could absorb alkali activator, leading to the formation of high-Ca gels and strengthening the interface.

Effects of binder proportion and curing condition on the mechanical characteristics of volcanic ash- and slag-based geopolymer mortars; machine learning integrated experimental study

Contradicting natures of volcanic ash (VA)- and ground granulated blast furnace slag (GGBFS)- based geopolymers with regard to their need for being exposed to a heating source for conducting alkali-reactions make meaningful differences in the strength and flowability of mortars. To address the impacts of types of the geoploymerizing agent, their proportions, and different curing regimes on their strength and shrinkage behavior, three different curing scenarios including curing at room temperature, RT curing; resting under room temperature for various curing periods, and then hydrothermally curing at an elevated temperature for one day, RO curing; and curing in the oven for one day and then resting at the room temperature, for various curing periods, OR curing, are considered. Based on the flowability, setting time, unconfined compressive strength (UCS), and drying shrinkage tests on eight different mixtures, the effects of binder proportion and curing conditions are evaluated. It was observed that with the substitution of 30% VA with GGBFS, specimens cured at RT condition outperformed OR specimens. This threshold was 45% while comparing RT and RO specimens and with higher slag content, RT specimens gain higher UCS. Also, for GGBFS proportion less than 45%, specimens cured at RO conditions showed higher long-term UCS compared to the OR specimens, and this behavior was reversed for higher GGBFS content. Scanning electron microscopy test results indicated that N-A-S-(H) type gel is the dominant geopolymeric gel in VA-based specimens, and as the amount of slag increases, the gels formed change to N-(C)-A-S-H and with further addition of GGBFS, C-A-S-H type gel is the dominant gel which results in strength development in GGBFS-based specimens. Based on the results of 80 UCS and 140 drying shrinkage tests, different machine learning (ML) algorithms and an evolutionary model were employed to present accurate and cost-effective predictive models as useful and capable methods for practitioners and researchers for the preliminary design stages of projects. A comparative study revealed the superior prediction efficiency of the gradient boosting (GB) model with the R2 score of 95% among 8 different ML algorithms and advanced ensemble models. In addition, evolutionary models with the coefficients of determination of 92% and 95% are, respectively, proposed for the drying shrinkage and the UCS. This study advances the field by assessing VA-GGBFS blend and curing effects on geopolymer mortars and developing ML-based models for compressive strength and drying shrinkage, facilitating efficient optimization in practical applications.

Synergic effect of recycled aggregates, waste glass, and slag on the properties of pervious concrete

The properties of pervious concrete made with coarse recycled concrete aggregates (RCA), recycled fine glass (RFG), and ground granulated blast furnace slag (GGBS) were examined. Pervious concrete was produced by substituting coarse aggregates with 0–40% RCA, fine aggregates with 0–100% RFG, and cement with 50% GGBS. Results revealed that incorporating RCA and RFG decreased slump and density but increased porosity and permeability. RCA replacement had a more noticeable negative effect on compressive strength, while RFG replacement was more impactful on splitting tensile and flexural strengths. Abrasion resistance decreased upon RCA inclusion and slightly increased with RFG incorporation. The performance of pervious concrete enhanced with GGBS addition. Its clogging potential was evaluated over a 30-year simulated lifespan. Permeability could be restored to half the original level. While RCA led to lower restoration rates, RFG and GGBS inclusions improved it. Analytical models were developed to correlate and predict the properties of pervious concrete.

Municipal woody biomass waste ash-based cold-bonded artificial lightweight aggregate produced by one-part alkali-activation method

The rapid industrialization process has resulted in the overconsumption of natural aggregates, leading to significant environmental concerns. Additionally, the disposal of municipal woody biomass ash (MWBA) has caused the depletion of land and further environmental pollution. Hence, production of artificial aggregate using MWBA is of great interest, as it reduces the consumption of natural aggregates and landfill area while recycling the MWBA. The main objective of this study is to determine the optimal mix design that can produce artificial aggregates with satisfactory strength and lightweight properties while maximizing the utilization of MWBA. Following that, the effects of different alkaline contents (9%, 12%, 15%) and ground granulated blast-furnace slag (GGBS) contents (0%, 10%, 20%, 30%) on the physical properties of the MWBA-based AAAs were investigated. Additionally, the pore distribution, phase and elemental compositions of the aggregates were examined to ascertain the mechanism of alkali-activation and strength development of the MWBA-based AAAs. The main result showed that at 15% Na2SiO3·5H2O content, increasing the GGBS content from 0% to 30% resulted in an increase in the loose bulk density and crushing strength of MWBA-based AAAs from 817 kg/m3 to 950 kg/m3 and from 0.84 MPa to 2.25 MPa, respectively, while decreasing the water absorption from 24.0% to 12.5%. This is due to the denser matrix observed, attributed to the GGBS addition, which enhances the effect of alkali-activation. Additionally, a new amorphous phase, namely C-A-S-H, was identified. The Si/Al ratio decreased with the GGBS content, resulting in more C-A-S-H gel formation and a denser microstructure with better performance for the AAAs. The novelty of this study is to demonstrate the feasibility of using MWBA in producing AAAs through a cold-bonded one-part alkali activation method. This method presents an alternative to natural aggregates that can be utilized in concrete.

Microstructural and optimization studies on novel one-part geopolymer pastes by Box-Behnken response surface design method

This paper reports the work on developing an optimized mix proportion of novel one-part geopolymer (OPG) binder produced by dry blending the solid aluminosilicate precursor and solid alkali source and then adding free water to the blended mix similar to the preparation of Ordinary Portland Cement (OPC). A three-level Box-Behnken Response Surface Method (RSM) design was used to study the properties of OPG mixes at fresh and hardened state and to test and develop the regression models. The Ground Granulated Blast Furnace Slag (GGBS) substitution, water to geopolymer solids (w/s) ratio, and the activator dosage were considered as the independent variables. The response target values were the flow value, initial and final setting time, and compressive strength. The multiple regression analysis with the quadratic polynomial model was used to fit the data, which offered an accurate and reliable match to the actual data. Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), and Fourier Transform Infrared Spectroscopy (FTIR) were used to study changes in microstructure, mineral phase, and molecular bonding of OPG mixes, respectively. Based on the material characterization observation, the change in GGBS addition, w/s ratio, and activator dosage were discovered to have a considerable impact on both the fresh and hardened properties. The optimum mix proportion obtained was 51.39% GGBS substitution, 0.32 w/s, and 12.35% activator content, with 191 mm flow, 68.56 MPa of compressive strength, 59 and 191 mins of initial and final setting time, respectively. The target values obtained using the one-part geopolymer mix with 50% GGBS substitution, 0.3 w/s, and 12% activator content were in close agreement with the target values predicted by the optimized mix, confirming the efficiency of RSM in obtaining the optimum one-part geopolymer mix proportion.

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

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

Characteristics of palm oil fuel ash geopolymer mortar activated with wood ash lye cured at ambient temperature

The development of geopolymer cement has gained recognition in recent years as an innovative cementitious material that can be used as an alternative for ordinary Portland cement. However, using aggressive chemicals such as sodium hydroxide (NaOH) as an alkaline activator and oven curing has limited geopolymer technology to laboratory research only. This study investigates the properties of a user-friendly geopolymer mortar produced using untreated palm oil fuel ash (POFA) and ground granulated blast furnace slag (GGBS) activated with wood ash (WA) lye and sodium silicate (Na₂SiO₃) under ambient curing conditions. The effectiveness of WA lye as an alkaline activator in geopolymer production was examined using three sets of liquid binder ratios (L/B) and five sets of alkaline activator ratios (AARs) to optimise the L/B and AAR. Using the optimised L/B and AARs, five combined groups containing 0, 10%, 20%, 30% and 40% GGBS were produced and tested for their rheological, mechanical and durability properties. Results show that the setting time and flowability of the mortar decreased with the addition of GGBS. The compressive and flexural strength of the investigated specimens were found to be in the range of 20.23–28.17 MPa and 4.04–4.48 MPa for 30% and 40% GGBS content, respectively. Moreover, the investigated durability properties improved with the increase of the GGBS content. In addition, the dense microstructure and geopolymerisation reaction products improved with the increase of GGBS content, as indicated in the scanning electron microscopy and Fourier transform infrared analyses. The study revealed that an economised user-friendly WA lye activated geopolymer mortar can be produced at ambient curing conditions by partially replacing untreated POFA with 30% GGBS, thereby eliminating the necessity of NaOH alkaline activator and oven curing.

Investigation of Post Fire Mechanical Performance of Recycled Aggregate Concrete Containing Ground Granulated Blast Furnace Slag

Structures made from recycled aggregate concrete are exposed to high temperatures during fire scenarios which degrade their mechanical properties. Hence, this study investigated the residual mechanical properties of recycled aggregate concrete (RAC) containing ground granulated blast furnace slag (GGBS) after exposure to elevated temperatures. 21 experimental runs for design mix of RAC considering recycled coarse aggregate (RCA) replacement of natural coarse aggregate at 50, 75, and 100%, GGBS replacement of cement at 0, 20, 40, and 60% and water to binder ratio at 0.4 and 0.5 levels were used. The residual mechanical properties of RAC including compressive strength, splitting tensile strength, and elastic modulus were determined through laboratory experimental tests at room temperature (about 25°C) and after exposure to elevated temperatures of 200, 400, 600, and 800°C. Experimental results showed that residual mechanical properties of RAC decreased with increasing temperatures but their resistance to degradation was significantly enhanced with the addition of GGBS at 40% GGBS content. The novel model developed for the prediction of residual compressive strength of RAC has high prediction accuracy based on the performance metrics used to evaluate the model performance. The model has p-values less than 0.0001, a high R² value of 0.9781, a low root mean square error (RMSE) of 1.456 and mean absolute percentage error (MAPE) of 0.2287. Overall, the study contributed immensely to the knowledge of RAC as a sustainable alternative to normal concrete in areas prone to exposure to high temperatures which will significantly aid the effective fire safety design of structural members produced with recycled aggregate concrete.

Compressive and Flexural Strength of Non-Hydraulic Lime Mortar with Slag (GGBS)

Mortar for masonry is important because it provides the bond between masonry units so enabling the composite to behave as a single material. The type of mortar used determines the flexural and compressive strength of the masonry. Currently, most mortars used in construction are cement based. However, due to the heavy energy-intensive processes that are involved in its production the cement industry is responsible for up to 10% of global CO2 emissions; therefore, there are serious environmental implications with the usage and application of cement mortars. A sustainable alternative are lime mortars which have 30% less embodied CO2. Lime mortars confer benefits in comparison to cement based mortars such as accommodating a greater degree of wall movement and improved damp resistance. The main disadvantage with lime mortars is the longer setting time which can take up to 91 days in addition to the low strength. A way to overcome this is to add cement replacements e.g pozzolans or slag. This paper investigates the properties of non-hydraulic (lime putty) lime mortar containing up to 20% ground granulated blastfurnace slag (GGBS). Findings show a minimal amount of GGBS addition of 2% doubles the mortar strength to 2 MPa within 91 days with an eventual strength of over 15 MPa achieved with 20% GGBS. Strengths satisfying minimum requirements for all four mortar designations were achieved with between 2 - 16% GGBS addition, all within 56 days ageing; with designations (i), (ii), (iii) & (iv) strengths being satisfied within 28 days. Therefore, non-hydraulic lime mortars with GGBS offer a more sustainable alternative to cement based mortars without compromising setting time or strength whilst offering improved flexibility and breathability

Low carbon binder preparation from slag-red mud activated by MSWI fly ash-carbide slag: Hydration characteristics and heavy metals' solidification behavior

Municipal solid waste incineration fly ash (MSWIFA) is hazardous, which safe disposal is a challenge. This study successfully prepared binder using MSWIFA and carbide slag (CS) as solid waste alkaline activators, stimulating the activity of red mud (RM) and ground granulated blast-furnace slag (GGBS). The properties and evolution mechanism of the binder were comprehensively evaluated in terms of compressive strength, fluidity, heavy metal leaching concentration, chloride ions' curing rate, and micromethods (XRD, SEM, EDS, and FTIR). The results show that CS and MSWIFA provide an alkaline environment for the hydration of RM and GGBS, promoting the formation of hydrated calcium chloroaluminate (HCC), ettringite, C-(A)-S-H gels and hydrotalcite (HT). At a mixing ratio CS: RM: GGBS: MSWIFA = 1:3:3:3, the binder had fluidity of 130 mm, 28 d compressive strength of 24.49 MPa and chloride curing rate over 80%. The environmental pH value mainly controlled the leaching risk of harmful components: its increase dropped the leaching rate of heavy metals. The addition of GGBS improved the structural compactness and buffering resistance of the matrix, effectively reducing the leaching risk of Cr and Zn heavy metals and keeping the leaching concentration of hazardous substances within the limits of national standards. This new binder system can be used to prepare pavement bricks and concrete blocks, mitigating solid waste environmental pressure and saving binder preparation costs.

Studies on the microstructure and durability characteristics of ambient cured FA-GGBS based geopolymer mortar

The present study involves evolving a mix proportion for geopolymer mortar cured at ambient temperature, utilizing the by-products of industries like fly ash (FA) and ground granulated blast-furnace slag (GGBS) as the binder. The parameters such as proportions of FA and GGBS, molarity of NaOH solution, Na2SiO3 /NaOH ratio, and alkaline liquid/binder ratio were considered. The consistency, setting time, and compressive strength for different percentages of FA replacement with GGBS were studied. It was observed that the addition of GGBS at 10–30 % is suitable for achieving the compressive strength at ambient temperature curing. Hence to assess the practical application of geopolymer mortar, microstructure studies at curing age of 90 days and durability tests over an exposure period of 180 days were conducted on F70:G30, F80:G20, F90:G10 mortar specimens and compared with ordinary Portland cement (OPC) control mixes. SEM, XRD, and FTIR results revealed the polymerization process in the geopolymer and hydration in OPC. Compared to F80:G20 and F90:G10 specimens, the microstructure of F70:G30 specimens containing a more significant proportion of GGBS showed a denser microstructure due to the increased C-A-S-H gel formation. TGA was used to determine the percentage of weight loss with the increase in temperature at curing age of 90 days. It was found that the extent of decomposition of compounds at high temperatures is lower in geopolymer mortar (F70:G30) than in OPC mortar. In addition, it was found that geopolymer mortar (F70:G30) has better resistance to water absorption, sorptivity, acid attack, sulfate attack, marine water attack, and chloride ion penetration and have equivalent mechanical qualities to the OPC control mix.

Treating Pb-contaminated clay slurry by three curing agents.

Each year, extensive dredged clay slurries containing heavy metals need to be treated before being reused; in such contaminated slurries, lead (Pb) is frequently identified. Quicklime (CaO)-activated ground granulated blast-furnace slag (GGBS), magnesium (MgO)-activated GGBS, and ordinary Portland cement (OPC) are usually used to remediate the lead (Pb)-contaminated soil; nevertheless, using these curing agents (or binders), particularly CaO-GGBS and MgO-GGBS, to treat Pb-contaminated slurry with high water content is rarely reported. Moreover, inconsistent results were obtained from previous studies in terms of the mechanical and leaching performance of Pb-contaminated soils with the three binders. Based on the above-mentioned reasons, this study used CaO-GGBS, MgO-GGBS, and OPC to treat the Pb-contaminated clay slurry, and compared the effectiveness of the three binders in improving the mechanical and leaching properties of the slurry. Laboratory tests were performed to examine the leaching, strength, mineralogical, and micro-structural performance of treated clay slurries. The results showed that GGBS-based binders were more effective than OPC in improving the strength and Pb leachability of contaminated slurries. When suitable ratios between activators (CaO and MgO) and GGBS were used, a similar or even higher UCS was produced by CaO-GGBS than MgO-GGBS. Similar leachate pH and Pb leachability could be achieved between CaO-GGBS- and MgO-GGBS-treated contaminated clay slurries. Therefore, it is not rigorous to state that MgO-GGBS is better in improving the strength and leachability of Pb-contaminated soils than CaO-GGBS only by comparing the two GGBS-binders based on the same activator/GGBS ratio, as reported in some previous studies. The leachability of Pb was affected by the pH, but the addition of GGBS facilitated the decrease of Pb leachability in slurries. The XRD result showed the formation of CSH and Pb(OH)2, which facilitated the reduction of Pb leachability.

Efflorescence mitigation in construction and demolition waste (CDW) based geopolymer

Using construction and demolition waste (CDW) as a raw material in geopolymer synthesis is gaining a growing interest owing to the dwindling availability of traditional aluminosilicate sources. However, CDW-based geopolymer (CDWG) is more prone to efflorescence due to the relatively low reactivity of CDW. Up till now, the efflorescence mitigation in CDWG has not been well documented. This study compared the effect of Al-rich admixtures, i.e., metakaolin (MK), and Ca-rich admixtures, i.e., ground granulated blast furnace slag (GGBS), on the efflorescence mitigation in CDWG. Results showed that both MK and GGBS addition significantly reduced the efflorescence formation of CDWG, but were based on different mechanisms. MK addition significantly decreased the number of excessive alkalis (from 24.5 to 10.2 mol%) through Al species introduction and N-A-S-H gels formation. Although GGBS addition only marginally reduced the excessive alkalis (from 24.5 to 19.9 mol%), it reduced the porosity and capillary water absorption of the geopolymer samples through C-A-S-H gels formation, hereby impeding the migration of alkalis and reducing the efflorescence extent. However, considering the risk of crystallization pressure and cracks induced by internal efflorescence in GGBS-containing samples, adding Al-rich materials (e.g., MK) is a better choice to mitigate efflorescence in CDWG. These findings also bring insights into efflorescence mitigation schemes and mechanisms of geopolymer sourced from other materials.