1. To assess the strength grade of cement mortar, the test piece of standard health 28d shall prevail. The test piece is a cube with a side length of 70.7 mm. The test piece 6 is a group, and the number of the prepared group should meet the following requirements:
1. The cement mortar of different cement mortar strength grades and different mix ratios shall be prepared separately, and the test pieces shall be prepared at random and shall not be selected.
2. Important and main masonry, 2 sets for each work shift.
3. General and secondary masonry, one set per work class.
4. The arch ring mortar should be prepared at the same time as the masonry conditional condition test piece to check the strength of each construction stage.
Second, the qualification standard of cement mortar strength
1. The average strength of the same strength grade test piece is not lower than the design strength grade.
2. The minimum strength of any set of test pieces is not less than 75% of the design strength level.
3. In the actual measurement project, when the cement mortar strength grade is rated as unqualified, the corresponding sub-project is unqualified. According to the "Masonry Structure Design Code" and "Masonry Engineering and Acceptance Specifications", the masonry mortar strength grade is 70.7mm × 70.7mm × 70.7mm test piece, after 20C ± 3C and humidity 60% ~ 80% The arithmetic mean of the compressive strength of 6 specimens for 28 days of curing was determined. The mortar is divided into 6 grades of M20, M15, M10, M7.5, M5 and M2.5. The mixed mortar should meet the type and strength grade of the design requirements, meet the requirements of the specified consistency, good water retention performance and uniform mixing. The mortar strength grade used for walls and columns subjected to vibration and height above 6M shall not be less than M2.5. The strength grade of masonry mortar in the cold area and the wet environment below the ground is generally increased by one level.
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