The basic oxygen furnace slag is a major waste by-product generated from steel-producing plants. It possesses excellent characteristics and can be used as a natural aggregate. Chemically, the basic oxygen furnace slag encloses free CaO and free MgO, which is the main reason for the expansion crisis since these free oxides of alkaline earth metals react with water to form their hydroxide yields. The objective of the present research study is to stabilize the basic oxygen furnace slag by using innovative geopolymer technology, as their matrix contains a vast quantity of free silicon, which can react with free CaO and free MgO to form stable silicate compounds resulting in the prevention of the basic oxygen furnace slag expansion predicament. Lab-scale and ready-mixed plant pilot-scale experimental findings revealed that the compressive strength of fine basic oxygen furnace slag-based geopolymer mortar can achieve a compressive strength of 30–40 MPa after 28 days, and increased compressive strength, as well as the expansion, can be controlled less than 0.5% after ASTM C151 autoclave testing. Several pilot-scale cubic meters basic oxygen furnace slag-based geopolymer concrete blocks were developed in a ready-mixed plant. The compressive strength and autoclave expansion test results demonstrated that geopolymer technology does not merely stabilize the basic oxygen furnace slag production issue totally, but also turns the slags into value-added products.

Geopolymer concrete is a useful alternative construction material for bridge deck systems, as it is characterized by a low carbon footprint, rapid setting, quick strength development, low cost, freeze-thaw resistance, low shrinkage, and sulphate and corrosion resistance. Heat curing enhances the mechanical properties of geopolymer materials (GPM), but it is not suitable for large structures, as it affects construction activities and increases energy consumption. Therefore, this study investigated the effect of preheated sand at varying temperatures on GPM compressive strength (Cs), the influence of Na₂SiO₃ (sodium silicate)-to-NaOH (sodium hydroxide—10 molar concentration), and fly ash-to-granulated blast furnace slag (GGBS) ratios on the workability, setting time, and mechanical strength properties of high-performance GPM. The results indicate that a mix design with preheated sand improved the Cs of the GPM compared to sand at room temperature (25 ± 2 °C). This was caused by the heat energy increasing the kinetics of the polymerization reaction under similar curing conditions and with a similar curing period and fly ash-to-GGBS quantity. Additionally, 110 °C was shown to be the optimal preheated sand temperature in terms of enhancing the Cs of the GPM. A Cs of 52.56 MPa was achieved after three hours of hot oven curing at a constant temperature of 50 °C. GGBS in the geopolymer paste increased the mechanical and microstructure properties of the GPM as a result of different formations of crystalline calcium silicate (C-S-H) gel. The synthesis of C-S-H and amorphous gel in the Na₂SiO₃ (SS) and NaOH (SH) solution increased the Cs of the GPM. We conclude that a Na₂SiO₃-to-NaOH ratio (SS-to-SH) of 5% was optimal in terms of enhancing the Cs of the GPM for sand preheated at 110 °C. Additionally, as the quantity of ground GGBS in the geopolymer paste increased, the thermal resistance of the GPM was significantly reduced.

Cold-Bonding Technique – A New Approach to Recycle Innocuous Construction Residual Soil, Sludge, and Sediment as Coarse Aggregates | InTechOpen, Published on: 2012-03-02. Authors: Chih-Ta Tsai

The role of 3R (Reduce, Reuse, and Recycle) in constructing the Eco-society or Eco-city has been comprehensively recognized and promoted worldwide over the past two decades. Nowadays, several hot issues such as the energy saving, CO2 reduction, and eco-society have received great attention. Approximately 40% of global energy is used in the construction and subsequent operation stage, while a large amount of construction waste is produced during construction and after demolition. In Taiwan, the government continuously makes great efforts to promote the development of green building materials produced with the recycling construction waste over the past decades. However, the recycling green building materials are not extensively accepted and used in the construction industry of Taiwan. The objective of this study is to propose a strategy for promoting the recycling green building materials through the investigation of “cradle-to-cradle” life cycle of construction products. The key factors lowering people’s impression and purchase behavior have been studied. The disadvantage of existing policy of government is also discussed and compared. Finally, the present study attempts to propose a feasible strategy to assist government to promote the utility of recycling green building materials.