【Daily Question】【Civil Engineering Version 20180529】

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Which of the following statements regarding the constituent materials of masonry mortar and their technical requirements is correct? ( ) A. For masonry mortar with strength grades of M15 and below, 42.5 grade ordinary Portland cement or masonry cement is recommended. B. The common fine aggregate for masonry mortar is ordinary sand. The silt content in the sand should not exceed 5%. C. When quicklime is transformed into slaked lime, it should be filtered using a mesh with an aperture of no more than 3mm×3mm, and the curing time must be at least 7 days ； The curing time for ground quicklime powder must be no less than 3 days. D. The calcium carbide slag used to produce gypsum should be filtered through a mesh with an aperture of no more than 3mm x 3mm; it must be heated to 700°C and held at that temperature for 60 minutes before use, and it can only be utilized once no acetylene odor is detected. Answer: B 【Explanation】For masonry mortar with a strength grade of M15 or lower, it is advisable to use 32.5-grade ordinary Portland cement or masonry cement. The common fine aggregate for masonry mortar is ordinary sand. The silt content in the sand should not exceed 5%. When quicklime is matured into slaked lime, it should be filtered through a mesh with an aperture of no more than 3mm x 3mm, and the maturation time must be at least 7 days ； The curing time for ground quicklime powder must be no less than 2 days. Calcium carbide slag used to produce gypsum plaster should be filtered through a mesh with an aperture of no more than 3mm×3mm. During testing, it must be heated to 700°C and held at that temperature for 20 minutes; it can be used only after no acetylene odor is detected.