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Calcium carbonate is wildly used in cementitious composites at different scales and can affect the properties of cementitious composites through physical effects (such as the filler effect, dilution effect and nucleation effect) and chemical effects. The effects of macro (>1 mm)-, micro (1 μm–1 mm)- and nano (<1 μm)-sizes of calcium carbonate on the hydration process, workability, mechanical properties and durability are reviewed. Macro-calcium carbonate mainly acts as an inert filler and can be involved in building the skeletons of hardened cementitious composites to provide part of the strength. Micro-calcium carbonate not only fills the voids between cement grains, but also accelerates the hydration process and affects the workability, mechanical properties and durability through the dilution, nucleation and even chemical effects. Nano-calcium carbonate also has both physical and chemical effects on the properties of cementitious composites, and these effects behave even more effectively than those of micro-calcium carbonate. However, agglomeration of nano-calcium carbonate reduces its enhancement effects remarkably.

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The usage of mineral basalt fibers is a relatively novel and popular topic nowadays due to its abundant availability, low cost, and higher temperature resistance. In addition, the establishment of analytical models is beneficial because the experimental work is more time-consuming and expensive. Therefore, in this study, the inorganic mineral basalt fibers with different length and content in hybrid fiber concrete composite are investigated to assess its suitability at room temperature and under high temperature. In addition, a new analytical model for stress-stain curve of hybrid fiber concrete composite is developed and compared with the models in previous studies.The microstructure examination is also conducted after exposure to high temperature to explore the fiber morphology and interaction with matrix. The substantial improvement was indicated by addition of basalt fiber in hybrid fiber concrete for stress-strain response, peak stress, elastic modulus, peak strain, ultimate stain, toughness, and specific toughness at room temperature and at 850 C. It was revealed that the basalt fiber had demonstrated overall good appropriateness in the hybrid fiber concrete composite for all the compressive properties. Moreover, the proposed analytical model could be useful for prediction of analytical behavior from experimental data under high temperature for the research and design purposes.