Concrete strength is not enough?

Concrete strength is not enough, poor homogeneity reason and solution
1, the reasons
(1) mixer metering equipment failure, slump is out of control, the concrete strength large discreteness.
(2) the cement expired or be affected with damp be affected with damp, activity;Sand, stone, aggregate gradation, gap is big, hydraulic, sundry, admixture use undeserved, content is not accurate.
(3) the improper concrete mixture ratio, and measuring,
(4) the construction of free water, make water cement ratio increases.
(5) concrete material order, stirring time is not enough, the mixing unevenness.
(6) winter construction, soon to dismantle or early seas.
(7) summer construction, specimen covering, failed to timely maintenance.
(8) the concrete block production not vibrating compaction, curing, poor management or curing conditions do not conform to the requirements, in the same condition maintenance, early dehydration or broken by external force.
2, prevention and control measures
(1) should be cement factory certification, fresh without aggregation, outdated cement with test qualified.Sand and gravel size, grading, and silt content should comply with the requirements, strictly control the concrete mixture ratio, guarantee the accuracy of the measurement, concrete mixing, should be in order the ensure mixing time and mix well.Prevent early concrete seas, friends in winter construction prepared with Portland cement concrete, the strength of 30% or more, slag cement mixing of concrete, strength of 40% or more, beginning to suffer freezing, according to the requirements of the construction specification carefully made on coagulation test block, and to strengthen the management and maintenance of block.
(2) to strengthen the maintenance of measuring equipment, to ensure accurate feeding control machine concrete mixture slump.Sampling
(3) the construction site should be in the process of mixing truck unloading 1/4 ~ 3/4 extraction, number of concrete quality inspection items needs to meet the 1.5 times, and shall not be less than 0.02 m3.Artificial dao forming block, should be two layers of load test, the thickness of each layer charging roughly equal, number of each layer in dao should be based on the cross section of the specimen, general every 2500 px2 cross-sectional area not less than 12 times.
(4) strengthen the block maintenance, standard specimen forming cover the surface, prevent moisture to evaporate, dehydration, the next day after ripping, should be put into the temperature is 20 + / - 1 ℃, humidity is more than 95% of the standard curing room maintenance.When without the raise room, concrete specimen can be in a temperature of 20 + 3 ℃ is not flowing water maintenance, the pH of the water should not be less than 7. Zhengzhou Xinfeng Machinery Co., Ltd. Main concrete mixer, concrete mixing station, stabilized soil mixing station, concrete batching machine, concrete conveying equipment, please call to discuss!