The quality of concrete quality, both for the safety of structure, but also the cost of structure has great influence, so we have to work on the construction quality of concrete has the enough attention.
1the strength of concrete and the main influence factors.
The quality of concrete is one of the main indicators of compressive strength, from the concrete expression of strength is not difficult to see, the compressive strength of concrete and concrete with cement intensity proportional to, according to the formula, when water cement ratio are equal, high strength cement than low strength grade of cement concrete compressive strength is much higher. In addition, water cement ratio and concrete strength is proportional, therefore, when water cement ratio is constant, attempted to use the addition of cement to improve the strength of concrete is wrong, you can only increase the workability of concrete, concrete increased contraction and deformation.
To sum up, the main factors affecting the compressive strength of concrete is the strength of cement and water to cement ratio, to control the quality of concrete, the most important is the control of cement and concrete water cement ratio of two main links. In addition, affect the strength of concrete and other factors not to be ignored.
Coarse aggregate on the concrete strength also has certain effect, when the stone of equal strength, gravel surface than a pebble surface roughness, it with cement mortar bonding than a pebble, when water cement ratio equal to or mix phase at the same time, two kinds of material preparation of the concrete, gravel concrete strength than a pebble is strong. Therefore we tend to aggregate control in about 3.2cm, fine aggregates on concrete strength influence extent than coarse aggregate small concrete formula, so no reflection sand flexible effect, but the sand quality on the quality of concrete has some influence. Therefore, gravel quality must accord with a concrete labeling the aggregate quality standards. As a result of construction site gravel quality change is relatively large, so the construction site must ensure that the gravel quality requirements, and according to the field of water content in sand timely adjust the water cement ratio, in order to ensure the concrete mix, not to be confused with the construction of experimental ratio ratio. Concrete strength only in temperature, humidity conditions can guarantee the normal development, according to the construction norms to curing temperature on the strength of concrete, have influenced the development of. Thermal insulation antifreezing in winter, summer to riot drying dehydration. Now winter construction general to take the comprehensive thermal storage method and steam curing method.
2concrete grade and average intensity and standard deviation of concrete relationship.
Concrete grade is based on the standard strength of concrete the overall distribution of the mean value minus1.645 times the standard value determination. It can guarantee the concrete identified are95% guaranteed rate, less than the standard value of the probability of not more than 5%, and fully guarantee the safety of building, from this presumption, sampling inspection of several groups of specimens to determine certain concrete average is equal to or greater than the concrete design level, its value depends on the quality of construction, which depends on the size of. The formula can be seen, the construction personnel should not only make the concrete is larger than the average to determine the grade of concrete, more important is to make every attempt to reduce concrete strength determines the variability, i.e., to try to make concrete standard deviation dropped to a low value, so, it guarantees the construction quality, but also to reduce the cost of project.
3key points for quality control of concrete
Quality control of concrete contains two basic elements:
3.1, make the concrete to meet the design requirements of the quality standard of.
In3.2, to meet the design requirements of the quality under the premise to reduce cost, these two requirements are actually reduce the standard deviation of concrete. The strength of concrete is discrete, this is objective, but through scientific management can control its minimum value, thus the concrete standard deviation can reflect the construction unit of the actual level of management, management level is high, the standard deviation is small.
Can say, concrete quality control is essentially a standard deviation control. To actually control the standard deviation from the following several aspects.
3.2.1, the rational design of concrete mix proportion. Reasonable mix ratio of concrete by laboratory experiment to determine, in addition to meet the strength, durability and can save the raw material, should be with construction of the required workability. Therefore to laboratory design reasonable formula, to provide qualified cement, sand, stone. Control of strength of cement, sand control fineness, moisture content, clay content, moisture content and mud stone control volume. Only the materials meet the eligibility requirements, in order to make a reasonable mix proportion of concrete, can make the construction is reasonable, to meet the design and acceptance criteria.
3.2.2, proper design mixture ratio construction. According to the construction mixing ratio and construction, we must first time determination of moisture content of sand, stone, will design mixture ratio conversion for the construction mixture ratio. Secondly, to use the weight, not volume ratio, finally, want in time to check whether the design of raw materials and raw materials conform to, this provided the requirements for two copies of the same material, a copy provided to the laboratory, a site to site, receiving personnel according to the sample receiving material, material and the sample does not match the Buddha, should immediately report to their superiors, timely change the mix ( material unqualified materials except).
3.2.3, strengthening management of raw material. Concrete variation will affect the strength of concrete. Therefore receiving personnel should strictly the quality pass, does not allow unqualified products to enter, and the other raw materials conform to timely reporting, take corresponding measures, so as to ensure the quality of concrete.
3.2.4, for measurement of concrete strength, our28 days strength shall prevail, for easy construction and quality assurance, we usually do 7 days of trial blocks, to concrete strength as far as possible according to their age determination of its development, in order to clearly determine its quality.
To sum up, from all aspects of quality control of concrete, to ensure the project quality, and ensure the credibility of enterprises and the long-term development.