Based on aluminum sulfate, a fluorine-free and alkali-free liquid accelerator (FF-AF-A) was prepared in this study. The setting time and compressive strength of three cement types with different FF-AF-A dosages were fully investigated. The compatibility of the FF-AF-A with the superplasticizers were also investigated, and the early hydration behavior and morphology of the hydration products of reference cement paste with the FF-AF-A were explored by hydration heat, X-ray diffractometry (XRD), and scanning electron microscopy (SEM). Test results indicated that adding the FF-AF-A at 8 wt% of the cement weight resulted in 2 min 35 s initial setting time and 6 min 30 s final setting time. The 1-day compressive strength of the cement mortar with 8 wt% of FF-AF-A reached 13.5 MPa, which represents an increase of 35% as compared to the strength of cement mortar without the FF-AF-A, and the 28-day compressive strength ratio was 119%. In addition, the FF-AF-A also showed good compatibility with different superplasticizer dosages. The results show that, when the FF-AF-A was added to the cement paste, it promoted the formation of ettringite crystals due to the aluminum ions (Al3+) and sulfate ions (SO4 2-) reacted with gypsum in the cement, as well as promoted the hydration of tricalcium aluminate (C3A) and tricalcium silicate (C3S) leading to the overall structure becomes more compact. As a consequence, the hydration heat rate of the cement sharply increased, the cement paste setting time is shortened, and the compressive strength of cement mortar is improved.

Shrinkage cracking of concrete at an early age has notable and adverse effects on the durability and long-term performance of the material because it damages surface integrity or undermines overall uniformity of concrete. In order to mitigate early-age concrete shrinkage cracking, a new gel-type superabsorbent polymer (SAP) has been developed as an internal curing agent (ICA). This paper investigates the effects of the introduced gel-type ICA dosage and curing conditions on early-age cracking mitigation of concrete. It is found that the cracking area of concrete is greatly reduced when up to $41\mathrm{kg}/{\mathrm{m}}^3$ gel ICA is used in concrete with water:cement ratio ($w:c$ ) of 0.5, and the internal relative humidity (IRH) of concrete at 7 days can be maintained at 92% or above. The gel-type ICA also is more effective in delaying initial cracking time and lowering the decreasing rate of IRH. It is believed that the superiority of this newly introduced ICA lies not only in its uniform dispersion in concrete but also in its molecular network structures, which contribute to maintaining moisture balance in the near-surface layer of concrete. This new gel-type ICA provides a new alternative way to control early-age cracking of modern concrete and it has a promising future in concrete construction, especially in windy, drying, and high-temperature areas.

The Electrolytic Manganese Residue (EMR) is a by-product of the electrolytic manganese metal (EMM) industry, containing high concentrations of potential pollutants such as NH₄⁺-N and soluble Mn²⁺. These components pose a serious threat to the ecological environment. To explore accurate, efficient, and harmless treatment methods for EMR, this study proposes a low-temperature thermochemical approach. The orthogonal experiment design investigates the effects of reaction temperature, reaction time, CaO, Na₂CO₃, Na₃PO₄, and water consumption on manganese solidified and ammonia removal from EMR. The results indicate that optimal conditions are a reaction temperature of 60℃ and a reaction time of 10 minutes. CaO precipitates Mn²⁺ as Mn(OH)₂, achieving effective manganese solidified and ammonia removal. The addition of Na₂CO₃ causes Mn²⁺ to form MnCO₃ precipitate, while Na₃PO₄ makes Mn²⁺ form Mn₃(PO₄)₂·3H₂O. Increased water consumption enhances the interaction adequacy between ions. Under optimal conditions (CaO 10%, Na₂CO₃ 1%, Na₃PO₄ 0.5%, and 80% water consumption), the removal rate of ammonium ions reaches 98.5%, and the solidification rate of soluble Mn²⁺ is 99.9%. The order of influence on ammonium ion removal is CaO > water consumption > Na₃PO₄ > Na₂CO₃. This study provides a novel approach for the efficient and environmentally friendly harmless treatment of EMR.