Study On Liquid Low-Alkali Shotcrete Admixture

Most of the rapid-set accelerators currently used in China are high-alkalinity powdery admixtures, which can do much harm to the eyes and skin of workers and adversely affect the long-term strength of concrete. What's more, powdery admixtures can't be used evenly in shotcrete. Therefore, it is necessary to develop a new kind of high-performance liquid low-alkali accelerator.Two kinds of liquid low-alkali accelerator were prepared in this paper: SL-1 and SL-2, which has an alkali content of 9.08% and 8.76%, respectively. At the W/C ratio of 0.4, 7.0% addition of SL-1 was added to King cement. The experiment showed that the cement paste could reach the initial set and final set in 3 minutes and 10 minutes, respectively; Id, 3d and 28d compressive strength of cement mortar were 19.8MPa, 32.7Mpa and 53.0MPa, respectively; 28d compressive strength ratio is 91.4% and its early-term strength is increased by 76.8%. 5.0% addition of SL-2 was added to a kind of cement called King Cement. It demonstrated that the initial set of the cement paste was 2.87 minutes and the final set was 5.5 minutes; Id, 3d and 28d compressive strength of cement mortar were IS.lMPa, 45.4Mpa and 55.9MPa, respectively; 28d compressive strength ratio was 96.4%; at Id, a 61.6% compressive strength gain was realized and only a 3.6% loss at later ages. Therefore, this kind of accelerator has the advantages of high early-age strength and low strength loss at later ages, which would definitely have an excellent prospective in popularization and application.A quantity of experiment on the properties of SL-1 and SL-2 was carried out in this paper. The adaptability of SL-1 with both various kinds of cement and UNF-5 superplasticizer was satisfying.What's more, when SL-1 was applied to Jingdu cement mortar and Lafarge cement mortar, it can increase their compressive strength at later ages. SL-2 accelerator only has good adaptability with P.O, and can favorably affect the compressive strength of Jingdu cement mortar and Lafarge cement mortar at later ages. Although its adaptability with superplasticizer was not as good as what we expected, it can be adjusted by increasing the addition of he rapid-set accelerators, or by decreasing the W/C ratio. Cement paste with either SL-1 or SL-2 accelerator can rapidly reach its setting time at low temperature. Appling SL accelerator and superplasticerzer at the same time,we can prepare C40 and C50 concrete easily.In addition, the accelerating mechanism of SL-1 and SL-2 accelerator was explored by the means of XRD and SEM. It demonstrated that these two kinds of accelerator not only can accelerate the hydration of CsA, but also can make the induction period of shorter, even disappearing.