Utilization of Sea Water to Production of Concrete in Terms of Mechanical Behavior

Supplies of fresh water in everyday life has increased, but the smaller the potential sources of water so we need to think of alternative uses of water for concrete construction work. This study aims to compare the compressive strength of concrete using sea water and fresh water with water cement ratio of 0.37. An experimental research was conducted by making specimens of concrete cylinder with a diameter of 150 mm and height of 300 mm. The study used specimens of concrete using sea water and fresh water. There were 32 specimens for each kind of concrete. The treatment of each specimen used sea water and fresh water in accordance with the type of mixing water. The immersion periods were 1, 3, 7 and 28 days. Mechanical testing of concrete was conducted by testing the compressive strength and elasticity, while the testing of concrete microstructure was conducted by using X-Ray Diffraction (XRD) and Scan Electron Microscopy (SEM). The results revealed that in the 28-day immersion period. The compressive strength values of the sea water concrete and fresh water concrete were 44.88 MPa and 44.03 Mpa respectively. The difference of compressive strength in the two types of concrete was not significant. The result of microstructure test in the 28-day period revealed that in the sea water concrete, there was a formation of Friedel’s salt (3CaO.Al2O3.CaCl2.10H2O) of 7.71%, tobemorite (3CaO.2SiO2.3H2O) of 58.66% and calcium hydroxide (Ca(OH)2) of 6.18%. In the fresh water concrete, there was a formation of tobermorite (3CaO.2SiO2.3H2O) of 51.35%, and calcium hydroxide (Ca(OH)2) of 22%. There was no formation of Friedel’s salt in the fresh water concrete because there was no mutual reaction between chloride and calcium hydroxide elements. From the regression analysis, showed that the difference of microstructure compressive strength differences caused by differences in the microstructure of the content of the two types of concrete.

KCl Extracted from Chlorine Bypass Dust as Activator for Plain Concrete

This study demonstrated the use of KCl separated from chlorine bypass dust (CBD) as an activator for plain concrete. The separated KCl was mixed with either ground granulated blast-furnace slag (BFS) alone, or a mixture of BFS and cement. The mixed paste of separated KCl and BFS set within 24 h, and exhibited a compressive strength of 22.6 MPa after 28 d. The separated KCl, cement, and BFS mixture exhibited a more rapid setting and a higher initial activity. Further, the compressive strength at 28 d was 57.7 MPa, which was 26.2% higher than that of the mixture without the activator. Water curing of samples with added separated KCl led to the generation of hydrocalumite, or Friedel’s salt. However, this hydrocalumite was decomposed while being cured under autoclave conditions at 180 °C. Overall, KCl was an effective activator for composite materials containing cement, and resulted in superior properties compared to mineral admixtures without an activator.

Effect of Ammonia-Soda Residue on the Strength and Chloride-Resistance Performance of Steel Slag-Granulated Blast Furnace Slag-Based Concrete after Immersion in Artificial Seawater

Ammonia-soda residue (ASR) is the main solid waste generated from soda manufacturing and is hard to reuse due to its complex chemical composition. This study investigated the influence of ASR content on the strength and chloride-resistance capacity of concrete based on basic oxygen furnace slag and ground blast furnace slag. The hydration and chloride resistance mechanisms were analysed by comparing the hydrate products and pore structural changes. The results showed that adding ASR had the greatest impact on early strength. ASR-introduced chloride ions may participate in the hydration process to generate Friedel’s salt and decrease ettringite. The optimum pore distribution appeared when the ASR-to-desulphurisation gypsum ratio was 2:3 because of the introduction of nucleation sites and the decrease of C–S–H gels. The two chloride resistance-capacity measurements were affected differently by the ASR content. The apparent chloride diffusion coefficient was mainly affected by the percentage of pores that were larger than 10 nm. However, electric flux increased when ASR increased due to the influence of introduced chloride. The crystallisation pressure of Friedel’s salt decreases the strength of concrete with ASR content after high-concentration artificial-seawater immersion. The significant chloride-resistance property provided an alternative use for the concrete containing ASR.

Reactive Transport Modelling of Chloride Ingress in Saturated Coral Aggregate Concrete

Utilizing coral aggregate concrete (CAC) for construction on remote islands can significantly reduce construction cost and period, CO2 emission, and consumption of non-renewable energy. The durability of reinforced CAC structures is critically influenced by their resistance to chloride attack. In this study, a reactive transport modelling was developed to investigate chloride ingress in CAC, in which a COMSOL-PHREEQC interface based on MATLAB language was established. The experiment from the literature was taken as a benchmark example. The results show that the developed numerical model can accurately predict chloride transport in CAC. Differing from ordinary aggregate concrete (OAC), Kuzel’s salt does not appear in cement hydrate compounds of CAC during chloride ingress. The numerical results indicate that the penetration depth of chloride in CAC gradually increases as the exposure time is prolonged. When CAC is exposed to an external chloride solution, the decrease in the pH of the pore solution affects the precipitation of Friedel’s salt, which is detrimental to the chemical binding of chloride.

Deterioration Caused By Sulfide-Bearing Aggregates: Performance Test Development

Recently in Quebec Canada, concrete structures suffered very rapid deterioration within 3 to 5 years of construction. The deterioration was caused by an iron sulfide, namely pyrrhotite, in the coarse aggregate that suffered oxidation inside concrete and promoted sulfate attack; indicated by the presence of ferric oxyhydroxides (“rust”), gypsum, ettringite, and thaumasite. The goal of the current work was to reproduce this reaction under accelerated laboratory conditions, in progression of a performance test. Conditions to promote pyrrhotite oxidation and internal sulfate attack were provided; exposure cycles were tested with heating and cooling, and saturation in oxidizing agents or lime solution. Oxidation was induced in concrete samples, however, other mechanisms contributed to deterioration. The bleach was found to promote NaCl and Friedel’s salt formation, furthermore, it seemed to mitigate expansion from sulfate attack. Sulfoaluminate decomposition was also found to cause secondary ettringite formation. More optimization to the test methods was recommended.

Deterioration Caused By Sulfide-Bearing Aggregates: Performance Test Development

Recently in Quebec Canada, concrete structures suffered very rapid deterioration within 3 to 5 years of construction. The deterioration was caused by an iron sulfide, namely pyrrhotite, in the coarse aggregate that suffered oxidation inside concrete and promoted sulfate attack; indicated by the presence of ferric oxyhydroxides (“rust”), gypsum, ettringite, and thaumasite. The goal of the current work was to reproduce this reaction under accelerated laboratory conditions, in progression of a performance test. Conditions to promote pyrrhotite oxidation and internal sulfate attack were provided; exposure cycles were tested with heating and cooling, and saturation in oxidizing agents or lime solution. Oxidation was induced in concrete samples, however, other mechanisms contributed to deterioration. The bleach was found to promote NaCl and Friedel’s salt formation, furthermore, it seemed to mitigate expansion from sulfate attack. Sulfoaluminate decomposition was also found to cause secondary ettringite formation. More optimization to the test methods was recommended.