The effect of elevated temperature and heating duration on high strength concrete with steel slag as cement replacement

A vast demand for concrete contributes to an enormous cement production where cement is the primary constituent in concrete manufacturing. Besides, the industry waste such as steel slag (SS) has produced in a large quantity and a large portion of it is disposed of on landfilling which causing a serious environmental impact. Utilization of the SS as partial cement replacement in producing concrete would reduce the cement consumption and amount of waste disposed. In addition, high strength concrete (HSC) is a heterogeneous composite which undergoes a transformation of physical, chemical, and mechanical behavior in a complicated way when subjected to elevated temperatures. The use of industrial by-products as supplementary cementitious materials in HSC has influenced the performance of itself after exposure to high temperature Thus, this research was conducted to investigate the effect of different heating temperatures and heating durations on HSC with the different particle sizes of SS as cement replacement based on the physical, chemical, and mechanical properties. Two different SS particle sizes were used as partial cement replacements which are fine SS (0.075mm) and coarse SS (0.15mm). At the early stage of the research, trial mix was conducted to identify the optimum water-cement ratio and SS replacement ratio. A control specimen and SS-HSC was cast into (100 x 100 x 100) mm cube, and (dia. 100 x 300) mm. After 28 days, the specimens were placed in the electrical furnace at temperature of 200℃, 400℃, 600℃ and 800℃ for 1, 2 and 3 hours. The physicochemical characteristic of the SS-HSC was examined by mass loss, color change, scanning electron microcopy (SEM), X-Ray diffraction (XRD), and thermogravimetric analysis (TGA). While the mechanical properties of SS-HSC were investigated by compressive strength test and modulus of elasticity. Besides, the results from compressive strength test and modulus of elasticity were used in mathematical modelling. In this study, Response surface methodology (RSM) was conducted to develop the mathematical model with various independent and dependent variables. The findings show that microstructure of HSC becomes denser when heated up to 400°C while the microcracks are found when subjected to 600°C and above. The residual compressive strength of SS-HSC is increased up to 400°C and decreased after exposure to 600°C and above. Furthermore, CSS10 obtained slightly higher relative residual compressive strength than FSS10 when heated at elevated temperature. The observed phenomenon could be attributed to the coarser particles size of SS acting as supplementary cementitious materials as well as aggregate in the HSC. From the RSM modelling, HSC subjected to elevated temperatures for 2 hours retains a significantly good performance on the mechanical properties while CSS10 presents a better post-fire behavior as compared to FSS10. The adjusted coefficient of determination (predicted R2) of the models are 0.9648 and 0.9126, respectively. Finally, the study showed that HSC that containing CSS has the potential to be used as structural application in fire resistance

Genetic and Functional Analysis of the DLG4 Gene Encoding the Post-Synaptic Density Protein 95 in Schizophrenia

Hypofunction of N-methyl-D-aspartate (NMDA) receptor-mediated signal transduction has been implicated in the pathophysiology of schizophrenia. Post-synaptic density protein 95 (PSD95) plays a critical role in regulating the trafficking and activity of the NMDA receptor and altered expression of the PSD95 has been detected in the post-mortem brain of patients with schizophrenia. The study aimed to examine whether the DLG4 gene that encodes the PSD95 may confer genetic susceptibility to schizophrenia. We re-sequenced the core promoter, all the exons, and 3′ untranslated regions (UTR) of the DLG4 gene in 588 Taiwanese schizophrenic patients and conducted an association study with 539 non-psychotic subjects. We did not detect any rare mutations at the protein-coding sequences of the DLG4 gene associated with schizophrenia. Nevertheless, we identified four polymorphic markers at the core promoter and 5′ UTR and one single nucleotide polymorphism (SNP) at the 3′UTR of the DLG4 gene in this sample. Genetic analysis showed an association of a haplotype (C–D) derived from 2 polymorphic markers at the core promoter (odds ratio = 1.26, 95% confidence interval = 1.06–1.51, p = 0.01), and a borderline association of the T allele of the rs13331 at 3′UTR with schizophrenia (odds ratio = 1.19, 95% confidence interval = 0.99–1.43, p = 0.06). Further reporter gene assay showed that the C-D-C-C and the T allele of the rs13331 had significant lower activity than their counter parts. Our data indicate that the expression of the DLG4 gene is subject to regulation by the polymorphic markers at the core promoter region, 5′ and 3′UTR of the gene, and is associated with the susceptibility of schizophrenia

The effect of particle sizes of steel slag as cement replacement in high strength concrete under elevated temperatures

This study investigates the impact of utilizing steel slag (SS) as a partial substitute for cement in high strength concrete (HSC) under high temperatures covering a range from 200 °C to 800 °C over a duration of 2 h. Two particle sizes of SS: 75 µm and 150 µm, were utilized as fine steel slag (FSS) and coarse steel slag (CSS). This study evaluates several physicochemical and compressive strengths of the HSC. After conducting the compressive strength, both residual compressive strength (RCS) and relative residual compressive strength (RRCS) were calculated. Scanning electron microscopy (SEM), Thermogravimetric analysis (TGA), and X-Ray Diffraction (XRD) analysis were carried out to analyze the physicochemical properties of HSC before and after subjected to elevated temperatures. The findings indicate an increase in the RCS of all specimens up to 400 °C. The replacement of FSS for cement enhances the compressive strength of HSC at ambient temperature, and FSS performs better than CSS up to 200 °C. However, beyond 400 °C, CSS exhibits a superior RRCS compared to FSS. XRD analysis confirms mineralogical changes in the HSC after exposure to fire, including the decomposition of C-S-H gel and the conversion of calcium hydroxide into calcium carbonate. The present study suggests that incorporating CSS in HSC has the potential to enhance its performance under high temperature conditions

Durability properties of mortar containing steel slag as supplementary cementitious material

The use of steel slag (SS) as supplementary cementitious material (SCM) is promising from the perspective of environmental protection and resource utilization. Previous studies have shown that using 20% SS replacement tends to decrease the strength of concrete. However, few studies have investigated the effect of SS on the durability properties of concrete, such as resistance to ammonium nitrate attack and resistance to sulfate attack. In this study, SS powder has been used as SCM with replacement ratio of 0, 10%, 20%, 30% and 40% to manufacture mortar. Compressive strength test, ammonium nitrate attack test and sulfate attack test have been conducted to investigate the properties of hardened mortar specimens. From this study, it is concluded that the increase in SS replacement ratio caused the decrease in mortar strength, the exposure to sulfate solution could increase the strength of mortar, and the exposure to ammonium nitrate solution led to the decrease in strength of mortar

The investigation on properties of sodium sulfate-activated mortar incorporating steel slag with various replacement ratio and particle size

The alkali-activated materials are alternatives for replacing Portland cement to manufacture concrete products, which has benefits on reducing carbon dioxide (CO2) emission and supporting the development of green sustainable construction. The combined use of steel slag (SS) and alkali activator (AA) to make alkali-activated concrete not only reuse the industrial waste but also improve the activity of SS. There are many types of chemicals can be used as AA, such as sodium silicate, sodium hydroxide, sodium carbonate and sodium sulfate (SST). In this study, SST was chosen as the AA, and the performance of alkali-activated mortar incorporating SS from 0 to 12.5% of Portland cement by mass, activated by SST with the dosage varying from 0 to 3% of cement by mass, was investigated. In addition, two types of SS, of which the particle sizes are less than 75 μm and 150 μm, were used to manufacture alkali-activated SS mortar. Flow table test, compressive strength test and flexural strength test were conducted to evaluate the fresh and hardened properties of alkali-activated steel slag (AA-SS) mortar. Response surface methodology (RSM) was used in this study as an analysis method. As result, the addition of SS tends to decrease the strength of mortar, while the addition of SST could lead to the increase in the strength of mortar

RSM-based modelling of cement mortar with various water to cement ratio and steel slag content

The water to cement ratio (w/c) has a direct effect on the hydration process of cement mortar. It basically dictates the workability and mechanical properties of cement mortar or concrete. Steel slag (SS) is one of the industrial by-products which is used in concrete as supplementary cementitious materials. Utilizing SS in concrete could mitigate the impact of the massive amount of concrete demand and promise an alternative to industrial waste management. However, previous studies show that steel slag has high water absorption during the mixing stage due to its grains' morphology. This study intends to determine the influence of SS content of 0%, 2.5%, 7.5%, and 12.5% (by mass) in cement mortar with 0.40, 0.45, 0.50, and 0.55 w/c ratios. A series of experimental tests were conducted to investigate the workability, compressive strength, flexural strength, and water absorption characteristic in this study. The results show that a 0.4 w/c ratio with 2.5% SS substitution presents a very low workability as compared to 7.5% and 12.5% SS content. Moreover, the higher substitution of SS in cement mortar has significantly decreased its strength. However, by decreasing the w/c ratio from 0.55 to 0.40, the strength is enhanced at 28 days. Based on the experimental results, response surface methodology (RSM) analysis was performed to develop the statistical model to predict the loss in cement strength as a function of the SS contents and w/c ratios. The predicted models are validated by examining the correlated coefficient of determination (R2). The R2 values for models of compressive and flexural strength are 0.9995 and 1.0000, respectively. From the results, it was confirmed that the incorporation of SS into cement mortar with a low w/c ratio has significantly increased the strength performance of the cement mortar

Investigation on the effect of steel slag as cement replacement material on mechanical properties of mortar

The use of SS to replace cement in mortar production can reduce the consumption of cement while improving the efficiency of the resource utilization. This study is to investigate the influence of SS as cement replacement material on the properties of fresh and hardened mortar. A series of mixes by varying the contents of SS from 0-40% with increment of 10% replacement ratio was prepared. Flow table test, compressive strength test and flexural strength test have been conducted. While for the compressive strength, it reduces from 19.7 to 4.2 MPa, 34.1 to 10.4 MPa, 41.5 to 13 MPa with the increase of SS replacement ratio for 1-day, 7-day and 28-day curing age mortar, respectively. Flexural strength value decrease from 5.7 to 2.5 MPa, 7.5 to 4.3 MPa and 8.2 to 5.6 MPa with the increase of SS replacement ratio for 1-day, 7-day and 28-day curing age mortar, respectively. The optimum mix design of SS mortar is 10% replacement ratio

Mechanical and water absorption properties of cement mortar incorporating basic oxygen furnace slag as fine aggregate

The steel industries produce much waste called steel slag (SS) which can be classified into three broad classification namely basic oxygen furnace slag (BOFS), electric arc furnace slag (EAFS) and ladle furnace slag (LFS). The disposal of these SS resulted in land occupation, water pollution and other environmental issues. The aim of this research is to study the performance of cement mortar by using BOFS as partial sand replacement. The properties of both fresh and hardened mortar containing 10%, 20% and 30% of BOFS with particle size <0.15mm were examined. The mechanical properties of BOFS mortars were tested at 1, 7, 28 and 60 days. While for water absorption, it was conducted only at 28 days. Results show that the increase of BOFS causes reduction in workability and water absorption which indicates good improvement in the water tightness of mortar. From the perspective of compressive strength, the replacement of BOFS increases the strength up to 14% compared to the reference specimen at 28 days. The compressive strength and flexural strength development in the mortar with 20% BOFS content yielded the highest strength gains compared to all specimens at later age

The effect of water to cement ratio on the fresh and hardened mortar containing steel slag as cement replacement material

The development of construction requires large amounts of resources which resulted in scarcity in good quality natural resources. Cement, being the main and widely used binder in the construction industry, are sourced from non-renewable source which causes negative impact to the environment. This study was conducted to evaluate the effect of SS on the fresh and hardened properties of mortar under conditions of different replacement ratio (2.5% and 12.5%) and water to cement ratio (w/c) (0.4, 0.45, 0.5). Flow table test, compressive strength test, flexural test and water absorption test have been conducted in this study. Results showed that flow table value of fresh mortar increased with the increase of w/c for both SS replacement ratio. Fresh property of mortar with lower SS replacement ratio was more sensitive to the variation of w/c. The increased w/c ratio has negative effect on the compressive strength and flexural strength of mortar specimens. Water absorption capacity of SS mortar increases with the increasing on w/c for both SS replacement ratio and the mortar specimens with higher SS replacement ratio has higher water absorption capacity at the same w/c level