In this paper, iron ore tailings (IOT) were separated from the tailings field and used to prepare cement stabilized macadam (CSM) with porous basalt aggregate. First, the basic properties of the raw materials were studied. Porous basalt was replaced by IOT at ratios of 0, 20 %, 40 %, 60 %, 80 %, and 100 % as fine aggregate to prepare CSM, and the effects of different cement dosage (4 %, 5 %, 6 %) on CSM performance were also investigated. CSM’s durability and mechanical performance with ages of 7 d, 28 d, and 90 d were studied with the unconfined compression strength test, splitting tensile strength test, compressive modulus test and freeze-thaw test, respectively. The changes in Ca2+ content in CSM of different ages and different IOT ratios were analyzed by the ethylene diamine tetraacetic acid (EDTA) titration method, and the micro-morphology of CSM with different ages and different IOT replaced ratio were observed by scanning electron microscopy (SEM). It was found that with the same cement dosage, the strengths of the IOT-replaced CSM were weaker than that of the porous basalt aggregate at early stage, and the strength was highest at the replaced ratio of 60 %. With a cement dosage of 4 %, the unconfined compressive strength of CSM without IOT was increased by 6.78 % at ages from 28 d to 90 d, while the splitting tensile strength increased by 7.89 %. However, once the IOT replaced ratio reached 100 %, the values increased by about 76.24 % and 17.78 %, which was better than 0 % IOT. The CSM-IOT performed better than the porous basalt CSM at 90 d age. This means IOT can replace porous basalt fine aggregate as a pavement base.

Porous basalt aggregate is commonly used in roadbed engineering, but its application in concrete has rarely been studied. This paper studies the application of porous basalt in concrete. Porous basalt aggregate is assessed for its effects on mechanical strength and durability of prepared C50 concrete; because it has a hole structure, porous basalt aggregate is known for its porosity, and porous basalt aggregates can be made full of water through changing the content of saturated basalt; after full-water condition is achieved in porous basalt aggregate mixture of C50 concrete, we discuss its mechanical properties and durability. The effects of C50 concrete prepared with basalt aggregate on the compressive strength, water absorption, and electric flux of concrete specimens of different ages were studied through experiments, and the effects of different replacement rates of saturated porous basalt aggregate on the properties of concrete were also studied. The results show that porous basalt aggregate can be prepared as C50 concrete. For early saturated porous basalt aggregate concrete, its compressive strength decreases with the increase of the replacement rate of saturated aggregate; this occurs up to concrete curing at 28 d, when the replacement rate of saturated basalt aggregate is greater than or equal to 40 %. The compressive strength of concrete increases with the increase of the replacement rate of saturated aggregate. The 28 d electric flux decreases with the increase of the replacement rate of saturated aggregate, indicating that saturated porous basalt aggregate can improve the chloride ion permeability resistance of concrete in later stages.

To solve the common problems of concrete preparation in low-temperature environments, calcium formate (C2H2O4Ca), anhydrous sodium sulfate (Na2SO4), triethanolamine (C6H15O3N), calcium bromide (CaBr2), and triisopropanolamine (C9H21NO3) are selected as early strength agents and mixed with C40 concrete in different dosages under low-temperature environments of 5 oC and 10 oC to develop a high-efficiency low-temperature compound early strength agent based on the effect of single-doped early strength agents. The effects of the compound early strength agent on the early strength of the concrete, the cement paste setting time, and cement fluidity at 5 oC and 10 oC are investigated, and the corresponding reaction mechanism is discussed from the perspective of micro-products. The best compound early strength agent ratio is found to be 2% of calcium formate + 0.08 % of TEA (C6H15O3N). The compound early strength agent effectively promotes the formation of hydration products, such as Ca(OH)2 and C-S-H gel. In comparison with the control group, the strength of the concrete cured for 18 h, 1 d, 3 d, and 7 d under simulated natural conditions at 5 oC increases by 700%, 540%, 11.4 % and 10 %, respectively, whereas at 10 oC, the corresponding values are 991%, 400%, 19.6 % and 11 %, respectively. The strength of the concrete at each age is close to the normal temperature standard of the curing strength. The addition of the compound early strength agent causes a reduction in cement fluidity and initial and final setting times, and also yields a good effect on the porosity of the early concrete.

In this article, poly methyl triethoxy silane was compounded with an inorganic waterproof admixture at a certain ratio to improve the performance of gypsum products; a new type of high-efficiency compound water-proofing additive was also investigated. Furthermore, the waterproof mechanism and the various properties on the hardened gypsum plaster were investigated in detail by XRD and SEM. The results show that the intenerate coefficient of gypsum plaster increased to more than 0.9; the water absorbing rate decreased to less than 10 %. Both the bending strength and the compressive strength of gypsum plaster increased by various degrees. The intenerate coefficient reached a maximum value of 0.73 and the strength of the samples showed almost no change when 5 % cement alone was added. In this new type of the high-efficiency compound with waterproof additive, the optimal technological parameters for formulas were obtained to be: 5 % cement, 18 % mineral powder, and 0.8 % poly methyl triethoxy silane, to compound gypsum plaster. Meanwhile, the production of high performance gypsum as a building material has become possible.