Expansive concrete are used to reduce cracking caused by drying shrinkage in concrete structures such as slabs, beams, columns, and pavement constructions. Although CaO and Sulphoaluminate based expansive agents have been used for decades, MgO-based expansive agents have demonstrated superior performance since 1970, especially for concrete dam structures. It has been proven that compensating shrinkage with MgO expansion efficiently prevents thermal cracking of mass concrete, reduces the expense of temperature control systems, and speeds up the construction process. This paper reviews several parameters such as reactivity, thickness of water film, curing condition, additive ratio, and calcination condition that affects expansibility, strength, soundness, durability, flowability, pore structures, crystal size, and hydration activity. The review indicates that the expansion characteristics of MgO may be designed flexibly by altering the calcination conditions (calcining temperature and residence time), maintaining a certain curing temperature, and tweaking its microstructure.

Geopolymerization is widely used in the construction sector for its characteristics of strong compressive strengths, quick hardening, long-term durability, fire resistance, and erosion resistance. This paper has gone through the geopolymer performances utilizing coal bottom ash (CBA), CBA blended with fly ash (FA), CBA mixed together with slag, and CBA with rice husk ash (RHA). CBA shows a better performance than FA in the compressive strength. This paper has discovered several elements that influence geopolymerization, the curing time, the curing temperature, the silicate and hydroxide ratio, and grinding CBA surfaces. The combination of CBA and RHA is suitable for lightweight concrete, as the range of the volumetric weight is within 1192 kg/m³ to 1655 kg/m³. The slump result decreases, as the ratio of CBA and slag increases. Slag particles are uneven in shape, which increases water consumption and leads to a honeycombed structure, whereas CBA particles are spherical in shape, which enhances workability.