Full
ZHANG Feng (1989-), male, Ph.D., Engineer. E-mail: fzhang@nhri.cn
Outline
A low-temperature early-strength accelerator was designed with three components, such as calcium bromide (CaBr2), lithium bromide (LiBr) and triisopropanolamine (TIPA). Effect of early-strength accelerator on the strength, setting time and fluidity of cement paste at a low temperature was investigated, and its mechanism of action was discussed based on the perspectives of hydration heat and product microstructure. The results show that the incorporation of low-temperature early-strength accelerator shortens the initial and final setting time of cement pastes, and accelerates the strength development of specimens at a low temperature (i.e., 5 ℃). The 1-d, 3-d, 7-d and 28-d compressive strength of cement pastes mixed with the low-temperature early-strength accelerator can be increased by 291%, 78%, 62% and 40%, respectively, and the strengthat each age after 3 d already exceeds that of the contrast sample cured at 20 ℃. At a low temperature, the early-strength accelerator can shorten the hydration induction period of cement hydration and advance the acceleration period. Furthermore, the maximum heat release rate can be increased by 78%, compared to the contrast sample. The cumulative heat release is increased by 227% and 52% at 12 h and 7 d, respectively. The early-strength accelerator can also promote the hydration reaction at the initial stage of cement hydration, increase the content of Ca(OH)2 in the sample and increase the hydration degree. Large amounts of Ca(OH)2 are formed in the products at the age of only 12 h, and some products, such as bromine-containing C-S-H gels and hydrated calcium bromoaluminate (Ca4Al2O6Br2·10H2O), are also generated. Large amounts of hydration products are accumulated, refining the pore diameter of the specimens at the initial stage of hydration (before 7 d) and decreasing the number of macropores. The total porosity of the cement pastes at 1 and 7 d is decreased by 16% and 31%, respectively, thus leading to the denser microstructure.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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