Compressive Strength of Sustainable Geopolymer Concrete Composites: A State-of-the-Art Review

The building industry, which emits a significant quantity of greenhouse gases, is under tremendous pressure due to global climate change and its consequences for communities. Given the environmental issues associated with cement production, geopolymer concrete has emerged as a sustainable construction material. Geopolymer concrete is an eco-friendly construction material that uses industrial or agricultural by-product ashes as the principal binder instead of Portland cement. Fly ash, ground granulated blast furnace slag, rice husk ash, metakaolin, and palm oil fuel ash were all employed as binders in geopolymer concrete, with fly ash being the most frequent. The most important engineering property for all types of concrete composites, including geopolymer concrete, is the compressive strength. It is influenced by different parameters such as the chemical composition of the binder materials, alkaline liquid to binder ratio, extra water content, superplasticizers dosages, binder content, fine and coarse aggregate content, sodium hydroxide and sodium silicate content, the ratio of sodium silicate to sodium hydroxide, the concentration of sodium hydroxide (molarity), curing temperature, curing durations inside oven, and specimen ages. In order to demonstrate the effects of these varied parameters on the compressive strength of the fly ash-based geopolymer concrete, a comprehensive dataset of 800 samples was gathered and analyzed. According to the findings, the curing temperature, sodium silicate content, and alkaline solution to binder ratio are the most significant independent parameters influencing the compressive strength of the fly ash-based geopolymer concrete (FA-BGPC) composites.

Developing New and Optimizing Current Test Methods to Evaluate SulphiDe-bearing Aggregate

This research focuses on testing the applicability on aggregates from Ontario of a testing protocol to evaluate the potential oxidation of sulphide-bearing aggregates, optimizing the protocol test methods, and develop new tests based on the obtained results. The protocol comprises of three sequential tests: Total sulphur content, Oxygen Consumption Test and Oxidation Mortar Bar Test. For the oxygen consumption test, using processing equipment with cast iron media, was found to contaminate the samples and produce high consumption. Moreover, controlling the tested aggregate gradation produces higher consumption and more consistent results than using a fine aggregate sample (<150µm) without controlling the minimum size. The oxidation consumption test showed lower expansion values for carbonate aggregates compared to aggregates with high silicate content. Exposing siliceous aggregate, whether alkali-silica reactive or not, to the high pH from the oxidizing solution and the high temperature produces high expansion regardless of the oxidizable sulphide content. As such, new expansion criteria are suggested which takes into consideration the silicate content of the aggregates. The dissertation proposes, based on testing twenty-six aggregates, modifications to: the oxygen consumption test; the expansion criteria of the mortar bar test; and proposes a new oxidation mortar bar test to avoid the limitation of the applicability of the original mortar bar test on siliceous aggregates. In the new testing program, different testing regimes were investigated using different oxidizing agents and environmental conditions that can promote oxidation of sulphide-bearing aggregates, without the promotion of other chemical reactions (Alkali silica reaction products or Friedel’s’ salt). Out of the various investigated tested regimes, two testing procedures showed promising results and recommended for further development and use. Bleach and lime water are used in these tests as the oxidizing agents; however, mortar bars in both regimes are stored at lower temperature compared to that of the original test in the protocol. Based on the expansion results, new expansion criteria are suggested that can detect if the aggregate contains oxidizable sulphides.

Developing New and Optimizing Current Test Methods to Evaluate SulphiDe-bearing Aggregate

This research focuses on testing the applicability on aggregates from Ontario of a testing protocol to evaluate the potential oxidation of sulphide-bearing aggregates, optimizing the protocol test methods, and develop new tests based on the obtained results. The protocol comprises of three sequential tests: Total sulphur content, Oxygen Consumption Test and Oxidation Mortar Bar Test. For the oxygen consumption test, using processing equipment with cast iron media, was found to contaminate the samples and produce high consumption. Moreover, controlling the tested aggregate gradation produces higher consumption and more consistent results than using a fine aggregate sample (<150µm) without controlling the minimum size. The oxidation consumption test showed lower expansion values for carbonate aggregates compared to aggregates with high silicate content. Exposing siliceous aggregate, whether alkali-silica reactive or not, to the high pH from the oxidizing solution and the high temperature produces high expansion regardless of the oxidizable sulphide content. As such, new expansion criteria are suggested which takes into consideration the silicate content of the aggregates. The dissertation proposes, based on testing twenty-six aggregates, modifications to: the oxygen consumption test; the expansion criteria of the mortar bar test; and proposes a new oxidation mortar bar test to avoid the limitation of the applicability of the original mortar bar test on siliceous aggregates. In the new testing program, different testing regimes were investigated using different oxidizing agents and environmental conditions that can promote oxidation of sulphide-bearing aggregates, without the promotion of other chemical reactions (Alkali silica reaction products or Friedel’s’ salt). Out of the various investigated tested regimes, two testing procedures showed promising results and recommended for further development and use. Bleach and lime water are used in these tests as the oxidizing agents; however, mortar bars in both regimes are stored at lower temperature compared to that of the original test in the protocol. Based on the expansion results, new expansion criteria are suggested that can detect if the aggregate contains oxidizable sulphides.

ANALYSIS OF NITRATE, PHOSPHATE, AND SILICATE CONTENT AND THEIR EFFECTS ON PLANKTONIC ABUNDANCE IN THE ESTUARY WATERS OF BATANG ARAU OR PADANG CITY WEST SUMATRA PROVINCE

The entry of nutrients (nitrate, phosphate and silicate) from land-based anthropogenic activities (industry, agriculture and household waste) through rivers can potentially cause changes in water quality and will affect fertility and aquatic organisms such as phytoplankton. These three nutrients play an important role in the living tissue cells of living organisms and in the photosynthesis process. This study aims to analyze the effect of nitrate, phosphate and silicate content on the plankton abundance in the estuary of the Batang Arau River, Padang, West Sumatra. The method used is a survey method, the determination of the sampling station is done by purposive sampling, data were analysed by Excel and SPSS Software. Based on the results of laboratory analysis, the nitrate content ranged from 0,117 to 0,485 mg/l, phosphate content from 0,239 to 0,704 mg/l, and silicate content from 0,031 to 0,685 mg/l. Planktonic diatom abundance in the estuary of the Batang Arau River ranges from 194 to 750 ind/l. The results of the statistical analysis of the effect of nitrate, phosphate and silicate with an abundance of diatoms are expressed by the equation Y = 743,019 - 481,828Nitrate - 199,552Phosphate - 172,971Silicate. This equation explains that the effect of nitrate, phosphate and silicate content on diatom abundance has an inverse or negative relationship, where nitrate, phosphate and silicate levels increase, the diatom abundance will decrease. The difference of content and the relationship between parameters analyzed in this research are discussed.

SILICON THERMAL WATERS AND THEIR IMPACT ON HUMAN HEALTH

The unique mineral thermal water has been researched. The composition of thermal water has been studied, its effect on human health has been described. This thermal water belongs to the hydrocarbonate-silicon type. The total silicate content is more than 120 mg/l, which is one of the highest rates for thermal springs in our country. The low solubility of silicic acid is compensated by the ability of silicon to form positively charged colloids, which neutralize microorganisms and promote the precipitation of heavy metals. Perhaps this factor is responsible for the insignificant presence of heavy metals in water. The medical indications and contraindications for this type of balneological treatment are described.

CONTENTS OF NITRATES, PHOSPHATES, SILICATES AND MISTAKES DIATOMS (Epiphytic) IN SEAGRASSES (Thalassia hemprichii) WATERS NIRWANA BEACH KECAMATAN TELUK NIBUNG KOTA PADANG SUMATERA BARAT PROVINCE

Epiphytic diatoms are diatoms whose lives are associated with plants, one of which is seagrass. Nitrates, phosphates and silicates are needed to support growth and development, especially epiphytic which attaches to seagrass leaves. The research was conducted in May 2018 in the waters of Nirwana Beach, Teluk Nibung Subdistrict, Padang City, West Sumatra Province. The aim of this study was to determine the relationship of nitrate, phosphate, and silicate content to the abundance of diatoms. The method used in this study is the survey method. Taking diatom samples is done by grinding the surface of seagrass leaves using a brush, while sampling nitrates, phosphates and silicates is done using a water sampler. The results of this study indicate that nitrate concentrations ranged from 1,250-1,255 mg / l, phosphate 0,031-0,570 mg / l and silicate 1,180-1,700 mg/l. The total abundance of diatoms ranges from 459-3446 ind / cm2, where the diatom genus that dominates at each station is Navicula, Isthmia, and Stephanopyxis. Based on statistical analysis shows that the content of nitrate, phosphate, and silicate has a positive relationship to the abundance of epiphytic diatoms.

In situ collection of dust grains falling from Saturn’s rings into its atmosphere

Saturn’s main rings are composed of >95% water ice, and the nature of the remaining few percent has remained unclear. The Cassini spacecraft’s traversals between Saturn and its innermost D ring allowed its cosmic dust analyzer (CDA) to collect material released from the main rings and to characterize the ring material infall into Saturn. We report the direct in situ detection of material from Saturn’s dense rings by the CDA impact mass spectrometer. Most detected grains are a few tens of nanometers in size and dynamically associated with the previously inferred “ring rain.” Silicate and water-ice grains were identified, in proportions that vary with latitude. Silicate grains constitute up to 30% of infalling grains, a higher percentage than the bulk silicate content of the rings.