Table of Contents
The application of concrete quality defects prevention and control has become an essential part of concrete construction. Concrete mixing plant concrete is often prone to problems in the mixing process, bringing trouble to the construction progress and construction quality. Now we analyze the causes of the problems that often occur in concrete mixing plant and give a series of ways to solve them.
Causes and solutions of pumped concrete collapse loss and slump instability problems
The causes of
Concrete admixtures and cement adaptability is not good to cause rapid loss of concrete collapse.
Concrete admixtures are not enough, slow setting, plastic effect is not ideal.
Hot weather, some admixtures fail at high temperatures; rapid evaporation of water; bubble overflow caused by the loss of fresh concrete collapse fast.
The initial concrete collapse degree is too small, and the unit water consumption is too small.
Site site and mixing station coordination is not good, so that the tanker truck pressure, traffic jam time is too long, resulting in excessive loss of concrete collapse.
Adjust the concrete admixture formula, so that it is compatible with the cement. Before construction, be sure to do the concrete admixture and cement adaptability test.
Adjust the concrete ratio, increase or reduce the sand rate, water consumption, the initial collapse of concrete adjusted to more than 200mm.
Add an appropriate amount of fly ash to replace part of the cement.
Increase the amount of concrete admixture, and adjust the slow-setting ingredients in the admixture (especially when the temperature is much higher than usual).
To prevent rapid evaporation of water, bubble overflow too fast.
The use of slag cement or volcanic ash cement.
Improve the water retention and cooling device of the concrete truck.
Summary of experience
For pumped concrete, especially pumped concrete and the problem of concrete slump loss in submerged pile foundation. Through the study and exploration of the test summed up a set of solutions to solve the problem with the actual situation. Such as communication with admixture manufacturers to improve and adjust the slow-setting ingredients in the admixture; adjust the construction time of concrete, try to avoid the construction in high temperature; in the case of poor road conditions on the construction right-of-way far away using the second feeding of admixture; use a large amount of fly ash concrete mix ratio construction, etc..
So that the concrete slump loss of this difficult problem, to get greater relief. Whatever the reason for the slump to become too small to pump or to meet the slump of the construction requirements, we can use the admixture to adjust the slump to achieve the required slump, to eliminate the bad habit of adding water to increase the slump to fundamentally determine the quality of concrete!
The causes of concrete prone to waterlogging, segregation problems and solutions
Easy to secrete when the cement fineness is large, low C3A content in cement easy to secrete, cement standard consistency water consumption is small easy to secrete.
The amount of cement is small and easy to secrete.
Low-grade cement than high-grade cement concrete easy to secrete (with the amount of admixture).
The same level of concrete, concrete with high grade cement is more prone to secretion than concrete with low grade cement.
Unit water consumption of large concrete easy to secrete, segregation.
Concrete mixture temperature is too high, especially in summer, high temperature, rapid hydration reaction, slump loss.
Concrete with low strength grade is prone to water secretion.
The concrete with small sand rate is prone to water secretion and segregation.
Continuous particle size crushed stone is smaller than the single particle size crushed stone concrete secretion.
Concrete admixtures of water retention, thickening, air-entraining poor concrete prone to secretion.
Concrete with excess concrete admixture is prone to secretion and segregation.
Some models of mixer trucks with poor mixing performance, after a certain distance of delivery, the initial discharge of the concrete mixture occurs obviously coarse aggregate floating phenomenon.
There is water in the mixing cylinder of the concrete mixing truck, which is not drained before loading or water is added to the mixing cylinder arbitrarily during the transportation process.
The fundamental way is to reduce the unit water consumption.
Increase the sand rate and choose a reasonable sand rate.
Hot summer, measures to reduce the temperature of the concrete mixture.
Increase the amount of cement or mix the appropriate amount of Ⅰ, Ⅱ fly ash.
The use of continuous gradation of crushed stone, and small needle flake content.
Improve the performance of concrete admixtures, so that it has better water retention, thickening, or moderate reduction in the amount of concrete admixtures (on-site only), if the mixing plant to reduce the amount of concrete admixtures, and may be out of concrete concrete collapse loss of new problems.
concrete mixer truck before unloading, should be in the medium and high-speed rotation of the mixing cylinder, so that the concrete mixture evenly after unloading.
Strengthen the management, after cleaning the mixer barrel of the truck, the water must be drained before loading. After loading, it is strictly forbidden to add water into the mixing cylinder at will.
The pumpability of concrete is poor to catch the bottom or the causes of the slab and solutions
Ratio selection does not meet the requirements of the pumping process on the ease of concrete.
The amount of cement is low.
The sand and stone gradation is not reasonable, the void rate is large.
The sand rate in the ratio is too small, the slump is too large, the concrete is easy to segregate.
Serious water secretion of the concrete easy to appear to grab the bottom or slab (sticky pot).
Concrete with a large amount of cement is easy to catch the bottom.
Concrete admixtures in large amounts of concrete easy to catch the bottom of the phenomenon.
Small sand rate, concrete easy to appear the phenomenon of slabbing.
Concrete admixtures with high water reduction rate, high water secretion rate, water retention, thickening, air-entraining effect of poor concrete prone to bottom grabbing or slabbing phenomenon.
Reduce the unit water consumption.
Increase the sand rate.
Add the right amount of admixtures such as fly ash, reduce the amount of cement.
Reduce the amount of concrete admixtures.
Increase the air-entraining, thickening, water retention function of concrete admixtures.
The concrete strength is not enough, poor homogeneity causes and solutions
The causes of
Mixer metering equipment failure, slump out of control, concrete strength discrete.
Cement is out of date or moisture, the activity is reduced; sand, stone aggregate gradation is not good, large voids, high mud content, debris, improper use of additives, inaccurate dosing.
Improper concrete mix ratio, inaccurate measurement.
Randomly add water during construction, so that the water-cement ratio increases.
The order of concrete addition is reversed, the mixing time is not enough, the mix is not uniform.
Prevention and control measures
The cement should have the factory certificate, fresh and no lumps, expired cement by the test qualified before use. Sand, stone particle size, grading, mud content, etc. should meet the requirements, strict control of the concrete ratio to ensure accurate measurement, concrete should be mixed in order to ensure that the mixing time and mix well. Prevent concrete from freezing early, winter construction with ordinary cement preparation of concrete, strength of 30% or more, slag cement preparation of concrete, strength of 40% or more, before suffering freezing, according to the requirements of the construction specifications carefully make concrete test blocks, and strengthen the management and maintenance of test blocks.
Strengthen the maintenance of measuring equipment to ensure accurate feeding, control the slump of the concrete mixture out of the machine.
Construction site sampling should be taken between 1/4 to 3/4 of the process of unloading the mixing truck, the quantity should meet the required amount of concrete quality inspection items 1.5 times, and not less than 0.02m3. manually inserted into the molding test block, should be loaded into the test mold in two layers, each layer of roughly equal thickness, the number of times each layer should be based on the cross-section of the test piece, generally per 2500px2 cross-sectional area Not less than 12 times.
Concrete Mixing plant quality control experience and recommendations
Concrete quality management control is indispensable in the concrete quality inspection, is the main means to ensure the quality of concrete. In the production of concrete, transportation until the whole process of construction, it has a role that can not be ignored, its main role has the following five points.
The good five, supervision of the three inadmissible: that is, the raw material inspection off, mix ratio design off, measurement off, concrete mixing plant time off, slump and strength off; unqualified materials are not allowed to use, measuring equipment is not allowed to produce, unqualified concrete is not allowed to leave the factory, to ensure that the concrete meets the quality requirements.
Strictly according to the specifications of random sampling, production of test blocks, according to the truthful report, in order to truly play the purpose of guiding the production.
Do a good job of prior control, prevention of quality accidents, through the quality inspection of raw materials and fresh concrete and quality supervision of the whole production process, timely grasp of the quality of concrete dynamics, timely detection of problems, timely measures to deal with, prevent the occurrence of engineering quality accidents, so that the quality of concrete in a stable state.
feedback information, through the analysis of the inspection data, grasp the quality of concrete and the law of change, to improve the concrete mix design, to ensure the quality of concrete, the full use of additives and admixtures, reduce costs, strengthen management, etc., to provide the necessary information and basis.