Blast Furnace Slag Content Research Articles

Effect of GGBS on Fly Ash Based Geopolymer Mortar at Ambient and Heat Curing

AbstractThis study investigates and shows the effect of incorporation of ground granuated blast furnace slag (GGBS) content in fly ash (FA) based geopolymer mortar by assessing the strength properties of geopolymer mortar in both ambient (25 °C) and heat (60 °C) curing. The percentage of GGBS is varied from 0% to 50% with FA in geopolymer mortar. Sodium silicate (SS) and sodium hydroxide (SH) solutions are used to activate the main binders. For all the mixes the alkali/binder ratio, molarity (M), and sodium silicate (SS)/sodium hydroxide (SH) ratio are fixed to 0.45, 12 M, and 2, respectively. The fresh property in terms of slump flow and other properties like compressive strength, water absorption, and dry density of the geopolymer mortar are determined. The result of this study shows that the inclusion of GGBS content in FA‐based geopolymer mortar significantly increases the compressive in both the curing conditions. Maximum compressive strength of 44.33 MPa is obtained when 50% GGBS is added to the mixes at a curing temperature of 60 °C.

Desert sand-high calcium fly ash-based alkali-activated mortar: Flowability, mechanical properties, and microscopic analysis

In this study, the reaction mechanism of desert sand-high calcium fly ash-based alkali-activated mortar under different influencing factors has been investigated. Different properties of the developed desert sand-high calcium fly ash-based alkali-activated mortar, such as flowability, compressive and flexural resistance, micro-morphological attributes, and reaction mechanism, were studied for alkali admixture (Na2O/b), sodium silicate modulus, and ground granulated blast-furnace slag (GGBS) content. The results indicate that too low and too high Na2O/b (2%, 10%) and sodium silicate modulus (0.4, 2.0) lead to poor flowability and compressive strength. The compressive strength of the specimens could reach more than 70 MPa for Na2O/b and sodium silicate modulus in the range of 5%–8% and 1.0–1.5, respectively. With the increase in GGBS content, the flowability of the fresh paste continued to decrease, whereas the compressive strength increased. Under the effect of alkali activation, the desert sand was partially dissolved, promoting the formation of C(N)-A-S-H gel to some extent. It is also found in this study that the iron ions in the high calcium fly ash partially dissolved and formed a rice-grain iron-rich gel, effectively filling the matrix pores.

Cryosuction Experiments on Concrete Containing Ground Granulated Blast-Furnace Slag: Influence of Temperature, Air Entrainment And Salt

Abstract Frost deterioration of concrete is an important durability issue for structures exposed to high degree of saturation, low temperatures and de-icers. The material can then be severely damaged with internal cracking and/or scaling of the surface, which can lead to e.g. reduced protection of the reinforcement and loss of load bearing capacity. Experiments with liquid uptake in concrete using different temperature cycles was made to study cryosuction. The material used was concrete with different air content and different replacement levels of ground granulated blast-furnace slag (GGBS). The concrete samples were preconditioned by capillary suction. Three temperature conditions were used: constant temperatures of +20 °C and -20 °C, and temperature that cycled between -20 °C and +20 °C. As liquid medium, deionized water and a 3% NaCl salt solution were used. Air entrainment generally increased the liquid uptake. The amount of GGBS and the NaCl concentration in the liquid did not have any significant impact on the liquid uptake in these experiments.

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.

Study on the mechanical performance of alkali residue-based light-weighted soil

In this study, a novel approach for reusing alkali residue is presented, whereby a lightweight soil is developed through a process of drying alkali residue. The mechanical properties of the alkali residue-based lightweight soil were investigated using compression, shear, and California bearing ratio tests. The results reveal that the compressive strength of the soil increases with the addition of ground granulated blast furnace slag, higher wet density, and increased curing time. Among these factors, the wet density exerts the greatest influence on compressive strength, followed by ground granulated blast furnace slag content and water–solid ratio. The secant modulus, cohesion, internal fraction, and California bearing ratio were found to be dependent on the mix proportion and curing time. A high-precision predictive model was developed for compressive strength, and the functional relationships between compressive strength and other mechanical properties were established, enabling accurate predictions of secant modulus, cohesion, internal friction angle, and California bearing ratio based on compressive strength.

Volumetric stability and elastic properties of concrete subjected to simulated service exposure conditions on road pavements

Expressway and highway pavements are exposed to intensive impacts of exploitation, including heavy vehicle traffic and environmental factors such as temperature and moisture along with the aggression of de-icing agents. Proper selection of mineral aggregates and design of the concrete mixture composition are important for the durability of the concrete pavement. Experimental tests were conducted on concrete under simulated service exposure conditions with external exposure to a 3% sodium chloride solution. The subject of the research was the expansion and elastic properties of air-entrained concrete made with siliceous aggregates from rocks containing moderate amounts of reactive minerals. The category of reactivity of coarse aggregates was uncertain, and in the fine aggregate was moderately reactive quartz sand. Under simulated service exposure conditions on road pavements, the significant expansion of concrete specimens and a significant decrease in the resonance elastic modulus up to 12.5% were observed. The tendency of concrete to expand was related to the presence of reaction products of reactive silica in the aggregate grains with sodium and potassium hydroxides in the cement paste [ASR], confirmed by microscopic observations. Replacement of Portland cement with CEM II/A-V 42.5 N cement and CEM II/B-S 42.5 N cement significantly reduced concrete expansion and improved the stability of elastic properties. In two of the nine concrete mixtures, the selected content of siliceous fly ash and granulated blast furnace slag, 18% and 30%, respectively, turned out to be sufficient to counteract the deleterious effects of the ASR under conditions of external contact with sodium chloride solution. A practical method for predicting the durability of concrete in the conditions in which the reactivity category of the aggregate from local natural resources is uncertain was established.

Microscale and macroscale strength behaviors of blast furnace slag- cement based materials: Modeling and analysis

Blast furnace slag (BFS) is used extensively as a cement replacement material, improving both the microstructure and the mechanical properties. How to optimize the content of BFS used without losing the mechanical properties of the composite is a very important theoretical problem. Essentially, the strength evolution of BFS-cement based materials is mainly dominated by the hydration reaction of the cementitious material. The formed hydration products bind the dispersed aggregate particles together, so that the material exhibits a certain strength and stiffness on the macroscopic scale. Exploring the microstructural evolution of BFS-cement based materials contributes to the understanding of the failure and instability process under external stress loading, and the optimization of proportion ratios to achieve optimum mechanical properties. Consequently, a better understanding of the microstructure evolution of BFS-cement based material is required. In this study, the microstructure of the BFS-cement based material was modeled using the discrete element method in combination with techniques such as thermogravimetric (TG) analysis and X-ray diffraction (XRD). In addition, mercury intrusion porosimetry and uniaxial compressive strength tests were performed to verify the reliability of the model. Finally, a series of mechanical simulations were carried out using the model. The simulated porosity and compressive strength were compared with the relevant experimental data with an error rate of less than 10%, showing the strong simulation capability of the proposed model. Through representative elementary volume simulation analysis, it is shown that the 30 wt% addition of BFS had a more positive effect on long-term strength, with an increase of approximately 5% compared to that of pure cement sample. The proposed model exhibited that the slag hydration reaction consumes portlandite (CH) and produces more cementitious calcium silicate hydrate (CSH) particles, resulting in the simulated 28d strength starting to be larger than that of pure cement. The established microstructure model of BFS-cement based materials provides a basis for predicting the strength structural.

Robust extreme gradient boosting regression model for compressive strength prediction of blast furnace slag and fly ash concrete

In this study, a novel machine learning (ML) technique, eXtreme Gradient Boosting (XG Boost), was employed to train an extremely precise ML model. The developed XG Boost model was highly interpretable, filling the gap and opening black boxes in the literature. The study provides further a simple and free user interface to support the design of normal- and high-strength Blast Furnace Slag (BFS), and fly ash (FA) concrete. The compressive strength of 1030 concrete mixes containing cement (C), BFS, and FA were collected and analyzed. The baseline model tend to overfit, with R2 values of 0.996 and 0.919 for the training and testing datasets, respectively. The hyperparameters of the model have been optimized using vector multi-objective optimization to maximize the prediction capability of the model. The optimized XG Boost model exhibited a superior prediction performance with R2 of 0.992 and 0.949 for the training and testing datasets. Based on Gini indexes and SHAP values, C, FA, water, and aggregate were the most significant model parameters. According to this study, the best BFS, FA, sand, and superplasticizer contents for concrete strength optimization were 100–200, 100–200, 600–800, and 7–13 kg/m3, respectively. The SP has a negligible effect on concrete's compressive strength at low water contents (less than 180 kg/m3), but a stochastic effect at high contents. The various chemical properties of high-range water reducers may have resulted in the randomly generated response in the current study.

Development of strain hardening cement based composite for concrete retrofitting purposes

The ever-increasing population in earthquake-prone areas necessitates the modification of both the current buildings and those that have already been damaged. Installing earthquake-resistant parts is required for this. In order to fulfill the continually expanding need for retrofitting materials that are both efficient and economical, civil engineers are under great pressure to develop novel new materials. A recent development in the construction sector is cement composites that harden under stress. Small particles and fibers are both used to make these composites. The chemical may enter the creep of the damaged structure without causing any vibrations. In order to restore the structure's original virgin strength, the mechanical and durability properties of the cement-based composite with strain hardening have yielded positive results. These qualities contributed to the success. The SHCC has also been used to connect deck slabs since the addition of fibers boosts the material's potential for abrasion resistance. These characteristics are provided through the incorporation of fibres. The combination of glass-fiber-reinforced polystyrene, (Ground Granulated Blast furnace Slag) and polyvinyl alcohol (PVA) fibers impacts the characteristics of a strain-hardening cement-based composite material has been investigated via experimentation, study, and analysis. A Ground Granulated Blast furnace Slag (GGBS) composition that varies from 10 to 30 percent has taken the place of the prior level of fly ash. PVA fibers with content levels of 2.0 and 3.0 percent, each measuring 12 mm in length, were employed in the experiment. These tests examined the compressive strength, tensile strength, and durability of a wide range of materials. The test findings reveal that although tensile strength and durability characteristics of the strain-hardened cement-based composite rose with a higher percentage of Ground Granulated Blast Furnace Slag (GBBS) content, compressive strength did not change significantly. It has been shown that better outcomes are obtained when PVA fiber content is greater. This is valid for both the mechanical strength and durability characteristics that different combinations have.

Effects of mineral admixture on properties of cement-based foam material developed for preventing coal spontaneous combustion

This study investigated the cement-based foam material (CBFM) used in mine fire-extinguishing materials by using a self-made compound foaming agent, water, cement, mineral admixture included fly ash (FA), blast furnace slag (BFS) and silica fume (SF), etc. The effects of mineral admixture type, dosage, foam content and water-binder ratio on the properties of CBFM were analyzed using the orthogonal tests, further determining the optimal ratio of CBFM. Moreover, the influence of mineral admixture type on the performance of the CBFM was analyzed by comparing the scanning electronic microscope and X-ray diffraction test. As a result, when the BFS content was 20%, the foam content was 2 times that of the cementitious slurry, and the water-binder ratio is 0.5, the overall performance of CBFM could be optimized. The surface morphology and mineral component investigation exhibited that CBFM with BFS as a mineral admixture had the more uniform closed-cell structure than FA and SF. Moreover, the novel material had the inhibitory effect on the transformation of calcium aluminate hydrate and hydrated calcium sulfoaluminate, which in turn could maintain the strength of the composite. The experimental results showed that the fire extinguishing and cooling effect of CBFM was better than that of traditional fly ash foam, and it could quickly cool down the temperature burning coal pile within 30 min. In addition, the solidification products of CBFM would form a wrapping layer on the surface of the loose coal pile, inhibiting the contact between coal and air, further preventing coal spontaneous combustion effectively.

Consolidation of phosphorus tailings and soluble fluorine & phosphorus with calcium carbide residue-mirabilite waste as a green alkali activator

Two alkalis of industrial solid wastes, calcium carbide residue-mirabilite (CCRM), were used as a green combined activator to consolidate phosphorus tailings and soluble phosphorus as well as fluorine through the alkaline activation process. The results based on XRD, FTIR, 29Si NMR and SEM indicated that most of the blast furnace slag (BFS) forms gels to consolidate phosphorus tailings, and the calcium silicate hydrate (C-S-H) gel dominated mechanical properties and immobilization of soluble phosphorus and fluorine. Comparing with the classical alkaline activators Na2SiO3 and NaOH, the CCRM activated materials displayed great competitiveness in mechanical properties with the order of NaOH < CCRM < Na2SiO3. Its maximum compressive strength reached to 10.9 MPa, and the compressive strength increased greatly with certain increasing content of BFS. In addition, the toxicity characteristic leaching procedure (TCLP) tests found the consolidation of risky soluble fluorine and phosphorus ions in the alkaline activation materials (AAMs) presented in the trend of CCRM > NaSiO3 > NaOH, and the tendency enlarges with increasing BFS addition, over 93.1 % and 98.9 % of soluble fluorine and phosphorus ions could be well fixed. Considering on the environmental and economic efficiency, mechanical properties, soluble phosphorus and fluorine immobilization, the CCRM is found a quite potential solid waste alkali activator for phosphorus tailings and soluble fluorine & phosphorus solidification.

Mass Concrete with EAF Steel Slag Aggregate: Workability, Strength, Temperature Rise, and Environmental Performance

Temperature control is the primary concern during the design and construction process of mass concrete structures. As the concrete production has an enormous negative environmental impact, the development of green mass concretes will eventually become as important as the thermal characteristics. Therefore, this paper investigates the use of Electric Arc Furnace (EAF) steel slag aggregate for the partial replacement of the natural aggregate in the production of mass concrete. The impact of EAF steel aggregate on mass concrete workability, strength, and thermal behaviour was analysed. In addition, a cradle-to-gate LCA study was conducted to evaluate the environmental footprint and sustainability potential of the tested mass concrete mixtures. The study results suggest that the use of EAF steel slag aggregate in combination with a low-heat cement with a high content of blast furnace slag can significantly lower the temperature, reduce the environmental impact, and increase the sustainability potential of mass concrete, while at the same time providing sufficient workability and compressive strength. The study results indicate that EAF steel slag can be upcycled into an aggregate for the production of green mass concrete mixtures.

Performance of Self-Compacted Geopolymer Concrete Containing Fly Ash and Slag as Binders

Geopolymers can replace cement and help reduce the environmental impact of concrete construction, but research is needed to ensure their mechanical properties, durability and practicability. The aim of this investigation is to examine the influence of ground granulated blast furnace slag (slag) content on the performance, at the fresh and hardened states, of fly ash (FA) based self-compacted geopolymer concrete (SCGC). For this purpose, four SCGC mixtures containing 450 kg/m3 of total binder were examined. The alkaline-to-binder ratio was 0.5 for all mixes. FA was substituted with slag at 0%, 30%, 50%, and 100% of the total binder content. The fresh properties in terms of flowability, passing ability, viscosity, and segregation resistance, as well as the mechanical properties in terms of compressive strength and splitting tensile strength, were quantified. The durability behavior of SCGC was also studied to determine sorptivity and long-term free drying shrinkage. The results confirm that slag adversely affects the workability of SCGC mixtures except for the resistance to sieve segregation. Performance of SCGC in hardened states is in general enhanced with slag inclusion but at increased shrinkage strain. Predictions of splitting tensile strength were made using the ACI 318, ACI 363, Eurocode CEB-FIB, and Lee and Lee models. The ACI 363 and Eurocode CEB-FIB models were found to be inaccurate, except for the 30% slag mix. Predicted values obtained from the Lee and Lee model were very close to the actual values of the FA-based SCGC mix. The results of this work could lead to more sustainable concretes using geopolymers instead of OPC.

Performance Investigation of Geopolymer Grouting Material with Varied Mix Proportions

Grouting materials require not only high ultra-early-stage strength of the stone body, but also proper working performances, such as high fluidity and fast setting time, as well as good stability. Compared with the traditional pure cement grout, geopolymer grouting material has the advantages of fast setting time, high fluidity, good slurry stability, and high early strength of the slurry stone body, which is beneficial to reuse solid waste resources and can be applied to the conditions of rapid construction or repair work to a certain extent. This paper presents an experimental investigation into the performance variation of geopolymer grouting material with varied mass fractions of raw materials, and the grouting performance of geopolymer material with optimal mix proportion is also presented. The study is implemented by employing the designed experimental schemes, focused on fluidity and setting times, as well as ultra-early-stage (4 h, 8 h, 12 h, 16 h, 20 h, and 24 h) mechanical strength. The experimental result demonstrates that both ground granulated blast-furnace slag (GGBS) content and the mass ratio of activator solution to solid have influence on the working performance of geopolymers, and both GGBS content and activator concentration have influence on the mechanical strength of geopolymers. Furthermore, the variance analysis demonstrates that the fluidity of geopolymer material is dominantly affected by the mass ratio of activator solution to solid, the setting time of geopolymer material is mainly influenced by GGBS content, and the mechanical strength of geopolymer material is mainly affected by activator concentration. Moreover, the recommended mix proportion of geopolymer grouting material is proposed in this study, in which the replacement rate of GGBS is 45%; the modulus and concentration of modified sodium silicate activator are 1.5 and 75%, respectively; and the mass ratio of activator solution to solid is 1.5. In the recommended mix proportion, the geopolymer material has excellent comprehensive performance to implement grouting operation, in which the compressive and tensile strengths of the stone body reach 12.2 MPa and 0.8 MPa in 4 h, and reach 21.2 MPa and 2.1 MPa in 24 h. The fluidity is 223 mm, the initial setting and final setting times are 50 min and 57 min, the slurry stability of geopolymer material is good without liquid precipitation, in which the setting time is far less than 2 h. This work provides the experimental foundations for investigating the performance of geopolymer grouting material, which is also expected to provide reference for the further application and promotion of geopolymer materials used for grouting operations in rapid construction or repair work.

Development of Environmentally Clean Construction Materials Using Industrial Waste.

The accumulated waste generated from industries severely affects environmental conditions. Using waste as a construction material or soil stabilization is an emerging area in the construction industry. Introducing new additive materials to strengthen local soils using industrial waste is an inexpensive and more effective method to improve the soil. In light of this, this study aims to develop environmentally clean construction materials for stabilizing natural loam (NL) using red mud (RM), blast furnace slag (BFS), and lime production waste (LPW). Nine different mixtures were prepared with four different combinations of RM (20, 30, and 40%), BFS (25, 30 and 35%), LPW (4, 6 and 8%), and various content of NL. X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), atomic absorption spectroscopy (AAS), and axial compressive strength were examined. The results indicated that the optimum strength was obtained from the sample containing 40% of RM, 35% of BFS, and 8% of LPW. The observed compressive strength of the sample for 90 days was 7.38 MPa, water resistance was 7.12 MPa, and frost resistance was 7.35 MP, with low linear expansion meeting the demands for first class construction materials of the Kazakh norms. The mineral composition analysis evidenced the lack of heavy metals contaminants and hazardous compounds. Based on strength and environmental performance, RM, BFS, LPW, and NL mix can be used as a road base material. This process is believed to reduce environmental pollution related to RM and BFS, and lower the road base cost.

The Influence of the Type of Cement on the Properties of Surface Cement Concrete.

The aim of this work was to reduce the carbon footprint of cement concrete by using multi-component cement with a high content of blast furnace slag. The analysis consisted of comparing the properties of the concrete mix and the hardened concrete made of the CEM I 42.5 R-NA cement commonly used in Poland and the CEM III cement with a large amount of blast furnace slag. The tests used cement in a constant amount of 380 kg/m3, granite aggregate of 2/8, 8/16, 16/22 mm and sand of 0/2 mm. As part of this project, detailed tests of the concrete mix and hardened concrete were carried out in terms of compressive, bending, fracture and frost resistance after 150 cycles of freezing and thawing, and the pore structure in hardened concrete was assessed according to PN-EN 480-11. The endurance tests were performed after 7, 28 and 90 days. On the basis of the obtained results, it was found that the highest compressive strengths above 70.2 MPa were obtained for concrete with CEM III, 64.5 MPa for concrete with CEM I. Additionally, for concrete with multi-component cement, smaller drops in compressive strength were obtained and a more favorable pore distribution in hardened concrete was obtained. Concrete intended for road surfaces can be made of both CEM I and CEM III cement, as they meet the requirements of the technical specifications for roads with heavy traffic of heavy vehicles.

Mechanical Strength and Chloride Ions' Penetration of Alkali-Activated Concretes (AAC) with Blended Precursor.

The purpose of this study was to investigate the properties of hardened alkali-activated concrete, which is considered an eco-friendly alternative to Portland cement concrete. In this paper, the precursors for alkali-activated concrete preparations are blends of fly ash and ground-granulated blast-furnace slag in three slag proportions: 5%, 20%, and 35%, expressed as a percentage of fly ash mass. Thus, three concretes were designed and cast, denominated as AAC5, AAC20, and AAC35. Their physical and mechanical characteristics were investigated at 28 and 180 days, as well as their properties of chloride ion transport. The modified NT BUILD 492 migration test was applied to determine the chloride ions’ penetration of the alkali-activated concretes. Improvement of mechanical strength and resistance to chloride aggression was observed with ground-granulated blast-furnace slag content increase in the compositions of the tested concretes. Mercury intrusion porosimetry tests provided insight into the open pore structures of concretes. A significant decrease in the total pore volume of the concrete and a change in the nature of the pore diameter distribution due to the addition of ground granulated blast furnace slag were demonstrated.

Effect of Various Fly Ash and Ground Granulated Blast Furnace Slag Content on Concrete Properties: Experiments and Modelling.

Concrete is known as the most globally used construction material, but it releases a huge amount of greenhouse gases due to cement production. Recently, Supplementary Cementitious Materials (SCMs) such as fly ash and Ground Granulated Blast Furnace Slag (GGBFS) have been widely used in concrete to reduce the cement content. However, SCMs can alter the mechanical properties and time-dependent behaviors of concrete and the early age mechanical properties of concrete significantly affect the concrete cracking in the engineering field. Therefore, evaluation of the development of the mechanical properties of SCMs-based concrete is vital. In this paper, the time development of mechanical properties of concrete mixes with various fly ash and GGBFS was experimentally investigated. Four different cement replacement levels including 0%, 20%, 30%, and 40% by fly ash and GGBFS as well as ternary binders were considered. Compressive strength, splitting tensile strength, flexural strength, and elastic modulus of concrete were measured until 28 days. Three additional concrete mixes with ternary binders were also cast to investigate the early-age autogenous shrinkage development until 28 days. In addition, prediction models in existing standards were used and compared to experimental results. The comparison results showed that the prediction models overestimated the compressive strength but underestimated the splitting tensile strength development and autogenous shrinkage. As a result, a model capturing the effect of fly ash and GGBFS on the development of compressive and splitting tensile strength is proposed to improve the prediction accuracy for current standards and empirical models.

Long-term carbon dioxide sequestration by concretes with supplementary cementitious materials under indoor and outdoor exposure: Assessment as per a standardized model

An experimental study was carried out on concretes designed with an ordinary Portland cement (CEM I 52.5 N), blended cements containing 23 wt% fly ash (CEM II/B-V 32.5 R) or 82 wt% ground granulated blast-furnace slag (CEM III/C 32.5 N), and partial substitutions of CEM I with fly ash (30 wt%) or ground granulated blast-furnace slag (30 and 75 wt%). Measurements were carried out on Ø11X22 cm specimens after 10.8 years of exposure, under indoor and outdoor exposure, to determine their carbonation rates and degrees of carbonation. The objective was to compare CO2 uptake calculated with the parameters measured experimentally to that calculated with parameters defined by a standardized model commonly used by construction engineering (EN 16757 model). The comparison showed that the model: (i) underestimates the carbonation rate (up to 61%), (ii) underestimates the degree of carbonation under indoor exposure (up to 49%) and overestimates it under outdoor exposure (up to 78%), and (iii) considerably underestimates the maximum theoretical CO2 uptake (up to 77%) for high ground granulated blast-furnace slag content. Consequently, the model underestimates the CO2 uptake under indoor exposure (up to 86%). However, the comparison showed a better correlation under outdoor exposure. Based on these results, some adjustments to the parameters defined by the standardized model were suggested to better account for effects of exposure conditions and supplementary cementitious materials, which should improve the CO2 uptake assessment.

The Optimization of Mix Proportion Design for SCC: Experimental Study and Grey Relational Analysis.

The optimization of mix proportions based on the targeted fresh and hardened performances of self-compacting concrete (SCC) is a foundation for its transition from laboratory research to industrial production. In this paper, the mix proportions of various SCC mixtures were designed by the absolute volume method with changes in the content of river sand and manufactured sand, the content of fly ash and granulated ground blast furnace slag (GGBS) and the maximum particle sizes of coarse aggregates. This experimental study was carried out to verify the workability, density and cubic compressive strength of SCC. The results show that SCC demonstrated good performance with appropriate mix proportions of manufactured sand and river sand. A hybrid effect of fly ash and GGBS appeared on the fresh performance of SCC with a constant strength, and the coarse aggregate with a smaller maximum particle size was beneficial to the workability but detrimental to the compressive strength of SCC. Finally, the optimization of the mix proportion of SCC was evaluated by grey relational analysis, in which the weight of the indicators was determined by the entropy method to improve the evaluation credibility. As a result, the optimal mix proportions of SCC were selected.