Mix Proportion Design And Performance Test Of PCCP Cover Mortar

PCCP has become the most commonly used pipe in long-distance water diversion projects in China due to its high internal and external pressure,simple installation,good joint sealing and superior impermeability.Industrial tests were carried out with vertical mortar roller shooting machine to study the effects of different roller shooting parameters and different proportions on the strength,water absorption,appearance quality and resilience of PCCP mortar(1)The roll injection parameters determine the speed of the whole running of the roller ejection system,and the overall running speed is too slow,which leads to the dense and thick formed mortar layer;The overall running speed is too fast,and the formed protective layer mortar layer is too thin;The whole running speed is in the condition of medium and high speed,the mortar layer formed is compact and the thickness is qualified and economical.(2)The distance between the roller and the tube surface is 30 cm,40cm and 50 cm respectively,and the engagement state of the roller is embedded,tangent and separated respectively.Under the condition that the occlusal state of the roller is determined,with the increase of the roller shooting distance,the strength and rebound rate of the formed mortar gradually decrease,and the water absorption rate gradually increases.When the distance between the two rollers is fixed,the closer the two rollers are engaged,the higher the strength and resilience of the mortar,and the lower the water absorption.(3)With sand cement ratio of 2.2,2.3,2.4,2.5,2.6 and 2.8,the strength of PCCP roller shot mortar decreases gradually with the increase of sand cement ratio,and the water absorption first decreases and then increases.The mortar with sand cement ratio of 2.2 has the highest 28 d strength and water absorption,and the mortar with sand cement ratio of 2.4 has the lowest 28 d water absorption.(4)With the decrease of sand cement ratio and the increase of moisture content of fresh mortar,the outer protective layer of roll formed mortar will appear circular concave convex marks.Under the premise of not affecting the strength and water absorption of mortar protective layer,the appearance of mortar protective layer can be improved by increasing the sand cement ratio and reducing the moisture content of fresh mortar.The test shows that the appearance quality of mortar protective layer is better when the moisture content of fresh mortar is not more than 8.2% and the sand cement ratio is not less than 2.4.(5)When the sand cement ratio is fixed at 2.4,the moisture content of fresh mortar increases from 5.8% to 8.3%,the 28 d strength increases with the increase of moisture content of fresh mortar,and the water absorption decreases with the increase of moisture content.(6)Steam curing is beneficial to enhance the early strength of mortar,but the increase of internal pores of mortar under steam curing leads to high water absorption and is not conducive to the development of late strength.The results show that the 28 d strength of mortar block under standard curing condition is the highest and the water absorption rate is the lowest;the 28 d strength of mortar cured by spraying water every other day is second only to standard curing;the 28 d strength of mortar cured by natural curing is 9.8% lower than standard curing.