Cement: The final setting time should be longer (more than 6 hours), and 325# slag and ordinary portland cement should be adopted. It is strictly prohibited to use quick-hardening cement, early-strength cement and cement deteriorated by moisture. The choice of cement brand should consider its quality stability, production quantity and transportation distance. Cement should have a certificate of approval before entering the site every time, and the setting time and label of cement should be sampled every 200T t.

Gravel: The crushing value should be no more than 30% and the maximum particle size should be no more than 30 mm The particle composition of gravel should meet the requirements of 2# grading in 2.2. 1.6 in JTJ 034-93. For the convenience of construction, 10-30 mm coarse aggregate, 5- 10 mm medium aggregate and 0-5 mm fine aggregate should be used. The crushing value of coarse aggregate, the screening of various granular materials (mainly to check the particle grading deviation of feed), the plasticity index of fine soil below 0.5mm and the particle content below 0.075mm should meet the requirements in JTJ 034-93. After the above materials enter the site, two samples shall be inspected every 2000m3. 2.0 Composition Design of Mixture

Powder content should not be too much. On the premise of reaching the strength, the minimum cement dosage shall be adopted, but not less than 4.0%.

Improve aggregate gradation, reduce cement consumption, so that the cement consumption does not exceed 6%.

The dosage of cement can be prepared in five ways: 4%, 4.5%, 5%, 5.5% and 6%.

Nine samples (minimum number) should be prepared for each dose.

The specimen must be kept wet at the specified temperature (20 2℃) for 6 days, and the unconfined compressive strength test shall be carried out after soaking 1 day, and the average value and deviation coefficient of the test results shall be calculated, and whether RX( 1- 1.645Cv) is greater than Rd (the design strength of this project is 3.5MPa). The design dose should be the minimum dose to meet the strength, not exceeding 6%.

According to the influence of design dose and test delay time on the strength of mixture, the delay time to be controlled is determined through experiments.

The actual amount of cement used in the construction site increased by 0.5% compared with the designed amount.