Concrete slump detection
1. Standard slump cylinders, bullet-type rams, shovels, rulers, trowels, scales, etc. made of metal materials for experimental tools.
2. Experimental procedure
(1) Wet the slump cylinder and other utensils, and place the cylinder on a rigid horizontal plate that does not absorb water, and step on the foot pedal with your feet to keep the slump cylinder in a fixed position when loading. (2) Load the concrete sample into the cylinder in three layers, so that the height of each layer after tamping is 1/3 of the height of the cylinder.
Each layer is tamped 25 times with a vibrating rod, vibrating and tamping is carried out spirally from the outward center, evenly distributed. The bottom layer should be vibrated to the end, and the other two layers should be inserted into the surface of the lower layer. The concrete on the top layer should be higher than the mouth of the cylinder. If the concrete is lower than the mouth of the cylinder during vibration, it should be added at any time. After the top layer is tamped, scrape the excess concrete and smooth it with a spatula.
(3) After removing the concrete on the bottom plate of the cylinder, lift the slump cylinder vertically and steadily. The lift-off process is completed in 5-10 seconds. It should be carried out continuously from loading to the lifting drum, and completed within 150 seconds.
(4) After lifting the slump cylinder, the difference between the height of the cylinder and the height of the concrete specimen after the slump is measured is the slump value of the concrete mixture. After the slump tube is lifted off, if the concrete collapses or shears on one side, it should be re-sampled and measured separately. If the above phenomenon still occurs in the second test, it means that the concrete is not easy to handle and should be recorded for future reference. . (5) Observe the cohesiveness and water retention of concrete:
Cohesion: Lightly tap on the side of the collapsed concrete cone with a ram. At this time, if the cone gradually sinks, it means good cohesion. If the cone collapses, the part cracks or segregates, then Indicates poor cohesiveness.
Water retention: evaluated by the degree of precipitation of the slurry in the mixture. When the slump cylinder is lifted, if more slurry is precipitated from the bottom, and the cone part leaks out due to loss of aggregate, it means that the water retention of the concrete mixture is not good. If there is no slurry or a small amount of slurry precipitates from the bottom after the cylinder is lifted, it means that the concrete mixture has good water retention.
3. The requirements for concrete slump in the code
(1) When the concrete strength level is less than C50, the slump should be less than 180 mm, and when the strength level is greater than C50, the slump should be greater than 180 mm; (2) When the specified concrete slump is less than 40 mm, the allowable deviation is ±10 Mm; when the specified concrete slump is 50~90 mm, the allowable deviation is ±20 mm; when the specified concrete slump is greater than 100 mm, the allowable deviation is ±30 mm; (3) The sampling frequency of the concrete slump test should be the same as the concrete The sampling frequency of intensity inspection is consistent. (4) The construction requirements of concrete slump shall be implemented according to the contract signed by the construction.