Minh Duc Hoang

This study proposes a building energy element technology system that addresses cooling loads, in response to rising average temperatures due to global warming caused by climate change. The study analyzes performance variations and energy-saving potential based on design parameters of individual element technologies, utilizing both simulation and field demonstration to derive an integrated Cooling Load Package System (CPS). The methodology comprises three key steps: (1) identifying and selecting element technologies suitable for optimal building design under subtropical climate conditions, (2) employing the building energy simulation software EnergyPlus v9.6.0 to evaluate the energy performance of each technology and establish prioritization based on energy-saving potential, and (3) conducting local climate validation through the construction of an outdoor demonstration site in northern Vietnam to assess the real-world energy-saving effectiveness of the proposed CPS.

Centrifugal concrete products are manufactured using specific technology that changes the concrete proportion during consolidation. The bleeding of water reduces the water-to-cement ratio and increases the compressive strength of concrete. This affects the strength of the concrete determined on conventional casted cylinders, cen trifuged hollow cylinders, and drilled cores from piles. This research determines the experimental conversion factor of 80 MPa concrete between casted cylinders and centrifuged hollow cylinders, which is 0.86. The factor between casted cylinders or centrifuged hollow cylinders and drilled cores (diameter of 57 mm and height of 57 mm) is 0.87 or 1.01, respectively. These coefficients can be used in production quality control. Practical verification of established factors was carried out on high-strength prestressed centrifugal piles. It shows that the experimental conversion factor gives more reliable and precise results in converting the strength of drilled cores than the factor recommended in actual national standards. Consequently, larger-scale research is needed to review the national standards or to compile guidelines for centrifugal concrete piles.

Expanded polystyrene lightweight concrete is a composite which can be made by adding expanded polystyrene aggregate in normalweight concrete (as matrix). The research was focused on the effect of properties and volume of the matrix on the properties of lightweight concrete. The results show that properties of structural polystyrene concrete, such as workability and compressive strength, depend on the aggregate size of the matrix. It also shows that decreasing aggregate size of the matrix is the effective way to increase workability and compressive strength of lightweight concrete. When the density of concretes decrease by 200 kg/m³, slump values decrease by about 20 to 30 mm with lightweight concrete mixtures using maximum particle size of 0.63 mm, while slump values decrease by about 40 mm with the mixtures using maximum particle size of 20 mm. At the same density, the compressive strength of the structural polystyrenre concrete significantly decreased when the coarse aggregate diameter greater than 10 mm. Therefore, coarse aggregates with diameter size are smaller than 10 mm was recommended to use for matrix. In the result, expanded polystyrene concrete with density from 1,400 kg/m³ to 2,000 kg/m³ and compressive strength more than 20 MPa for structural application was made.

Fly ash is an industrial waste from coal-fired thermal power plants whereas red mud is an industrial waste generated during aluminum production from bauxite. If both fly ash and red mud are not properly managed, they could cause negative impact on the environment. This study utilized red mud and fly ash in combination with sodium silicate solution to produce a geopolymer-based material which can be used as building materials. This study focussed on the leachability of heavy metals in the raw materials and the geopolymer as this would be significant in assessing the environmental impact of the product. Leachability of heavy metals such as Cu, Zn, Cd, Pb, Fe, and Cr was evaluated based on European standard (EN 124572 – 2, EU CEN TC292/ CEN TC 308) with pH values at 7. The results showed that raw materials (red mud and fly ash) have higher leachability than geopolymer specimens. And the values of leaching tests for heavy metals in the geopolymer - based materials belonged to limits of EULFD and USEPA.

In this study, the alkaline solutions (NaOH) with concentration from 1M to 10M, red mud (RM) and silica fume (SF) were used as reactors in geopolymer reactions. RM contains 7.40% SiO₂ and 13.65% Al₂O₃, SF has 94.50% SiO₂, but only the activated oxides can participate into the geopolymer reactions. The activity of the oxides was investigated by measuring the dissolution of RM and SF in different concentrations of NaOH. Characteristics of the geopolymer samples were tested for compressive strength and softening-coefficient, its microstructure was analyzed by using X – ray diffraction (XRD). The experimental results were indicated that activated SiO₂ is the highest exist in SF. In the structure of geopolymers, the silica can be bonded directly to each other (Si-Si) or linked through “most” oxygen (Si-O-Si) to form independent polymer chains, while aluminum themselves cannot create independent polymer chains, it only can be replaced the Si atomic in Si-O-Si polymer chains (Si-O-Al), instead.

Geopolymer is an inorganic polymer material formed from alumino-silicate structures. Geopolymer has many outstanding functions in comparison with ordinary materials such as high mechanical strength, high heat and chemical resistance, and lightweight property. The engineering properties of geopolymer-based materials depend on raw materials and synthesized conditions. In which, the aluminosilicate materials having high activity and consisting of many alkaline activators have the possibility of increasing pH in geopolymer paste. In the solution of paste, aluminosilicate compounds are solubilized and then react with alkali-activated ions to form geopolymeric networks. The geopolymer can be synthesized in many different conditions depending on factors of temperature, pressure, and curing conditions. In this study, red mud (RM) was used as the main alumino resource for geopolymerization process. RM is a solid waste residue being left from the mining process of bauxite ores with caustic soda for alumina production. Its disposal remains a global issue in terms of environmental concerns. Formation of RM-based geopolymer was affected by many factors, in which, the alkaline activators are the most important factor. This research was conducted with sodium hydroxide and sodium silicate solutions to elucidate the effect of alkaline activator ratio to the engineering properties of RM-based geopolymers. The results showed that the RM-based geopolymer used sodium silicate solution has more outstanding properties than RM-based geopolymer using sodium hydroxide solution.

In this study, the alkaline solutions (NaOH) with concentrations from 1M to 18M, red mud (RM) and silica fume (SF) were used as reactors in geopolymer reactions. RM contains 7.40% SiO2 and 13.65% Al2o3and SF has 94.50% SiO2, but only the active oxides can participate in the geopolymer reactions. The activity of the oxides was investigated by determining the compressive strength of the samples under different curing conditions. The characteristics of the geopolymer samples were determined by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermo-gravimetric analysis (TGA)/differential thermal analysis (DTA) and nuclear magnetic resonance analysis (NMR). The experimental results indicate that active silica mainly exists in SF. In the structure of geopolymers, the silicon can bond directly with each other (Si-Si) or be linked through ‘bridging’ oxygen (Si-O-Si) to form independent polymer chains, while aluminium atoms can only replace the silicon atoms in Si-O-Si polymer chains to form Si-O-Al instead.