The infrequent setting behavior and hydration process of a Portland cement with very low alkali content were concerned. Gypsum and K₂SO₄ with different quantities and ratios were added into cement to adjust its sulfate and alkali content. The setting time and compressive strength of cements were tested, the hydration process and hydrates of cements were investigated by isothermal calorimetry, non-evaporable water content and XRD. The results show that gypsum addition is incapable of delaying the quick initial setting of the cement clinker. A moderate substitution of gypsum by K₂SO₄ in same reasonable sulfate content can promote the dissolution of gypsum, suppress the formation of h-AFm, and therefore prolong the initial setting time of the cement. Moreover, the Portland cement clinker shows a very hysteretic hydration exothermic process, accompanying with a hysteretic finial setting and a weak mechanical property in early age. An appropriate dosage of gypsum can promote the hydration of the cement and result in a reasonable final setting behavior and satisfactory strength development. The modification of gypsum on the properties of cement is influenced by its alkali content. The measures which could accelerate the sulfate-supply in cement is necessary to acquire a favorable hardening property when the cement with low alkali content is used in projects.

Ground granulated blast-furnace slag (GGBS) can be used as the hydraulic phase in alkali-activated slag cement (AAS) or as partial replacement in blended cements, whose storage conditions need to be fully assessed before practical applications. This paper tries to address this problem by storing the GGBS at the controlled relative humidity (RH) using saturated solution methods at 20°C. Followed by performing the dissolution experiments in both deionized water and NaOH solution on the obtained GGBS, where both aqueous and solid phases are characterised. The experimental results indicate that the GGBS stored in a high RH will depress the dissolution of silicate networks, thus suppressing the formation of C-S-H phases, especially in the NaOH solution. The dormant period of GGBS hydrated in DI water is positively correlated to the storage RH. From the degree of hydration point of view, the RH less than 60% should be recommended for storing GGBS. However, if the faster hydration of GGBS is the purpose when it is used as an SCM or in neutral salt activated cements, an extreme low RH should be recommended. It is also found that the increased storage RH shows the potential for increasing the inner products of hydrated GGBS.

Self-compacting geopolymer concrete (SCGC) is a revolutionary concept in the construction industry. This study fills the research gap by determining the impact of six different types of commercially available superplasticizers on the flow properties, dry density and compressive strength of SCGM. It was investigated that the relationship between rela-tive flow area (Gm) and relative flow speed (Rm) of SCGM depends on the type of superplasticizer. The test results ex-hibited that a polyaryl ether-based superplasticizer performed better in increasing the flow deformability and flow speed of SCGM in comparison to melamine-based and naphthalene-based superplasticizers. The excessive increase in air content of SCGM paste with the addition of some superplasticizers had a negative impact on the flow properties. The increase in sodium oxide to silica molar ratio (Na₂O/SiO₂) and sodium oxide to water molar ratio (Na₂O/H₂O) both had a negative impact on the flow properties of SCGM. It was determined that beyond a trigger value of Na₂O/SiO₂ of 0.171, the impact of the superplasticizer in separating the flowing particles of SCGM became insignificant, resulting in the flash setting. Moreover, the addition of each type of superplasticizer had a negative impact on the dry density and compressive strength of SCGM.

The study investigates the effects of the particle size distribution (PSD) of aggregates on the properties of calcium carbonate concrete (CCC). Fifteen different types of aggregate PSDs were designed to select the appropriate PSD for CCC, based on the experimental data. Notably, the compressive strength of the CCC depends on the aggregate PSD, fineness modulus of the aggregates, packing ratio, and the amount of solution moving throughout the specimen. After one-day CCC processing, its compressive strength reached 7.2 MPa with an appropriate PSD. In addition, the X-ray diffraction and scanning electron microscopy analysis revealed that aragonite was the dominant contributor to the development of CCC strength. The amount of aragonite was influenced by the amount of solution passing through the specimen and the PSD of the aggregate blend.