Factors causing quality problems in commercial concrete production and countermeasures

1 Quality control of raw materials

If you want to make a good product, you must have good parts. For example, BMW is made up of thousands of parts. If its parts are inferior, there is no famous brand car. Therefore, we should start with raw materials to improve quality. The raw materials of commercial concrete are composed of cement, mineral powder, fly ash, gravel, sand, admixture and water.

1.1 Cement

The strength of cement plays a very important role in concrete. Cement is the cementing material in concrete, and its strength directly affects the strength of concrete. If there is a problem with cement, there will be a problem with concrete. Therefore, the control of cement quality is very important. Cement quality control mainly includes cement warehousing management and cement inspection.

1.1.1 Cement warehousing. In the past, there were many concrete mixing plants where the concrete strength was too low. Finally, it was found that the reason was that the fly ash was hit into the cement tank. Once this phenomenon occurred, the consequences were very serious. Now, the author has formulated a plan to strictly control the warehousing of cement.

First, two locks are added at the entrance of the cement tank, one is managed by the weighing room staff and the other is managed by the laboratory quality inspector. The cement shall be weighed before entering the factory, and then the driver shall take samples. The sample, certificate of conformity and 3-day test report of cement shall be sent to the laboratory. The laboratory personnel shall open one of the locks and notify the weighing personnel to open another lock after opening. In this way, if one lock is opened incorrectly or not, the cement cannot enter the warehouse. Only two people in two departments can enter the warehouse after they have opened the right locks, so as to prevent the occurrence of accidents.

1.1.2 Cement inspection. The laboratory has a complete set of quality control system, from warehousing, inspection, sample retention and destruction of concrete raw materials, there should be a register and account. The cement samples shall be registered in the warehouse ledger before re inspection. Each batch of cement must be inspected once. The re inspected samples shall be labeled and sent to the sample room for storage for three months. After three months, if the strength is qualified, they can be destroyed. Each batch of cement shall be well documented, and once problems occur, we can find out where the problems are from the source.

1.2 Mineral powder

The mineral powder is also an important cementing material in concrete. The mineral powder is the slag produced in the smelting process of the steel plant, which is refined into powder after quenching. The activity index of mineral powder represents the quality of mineral powder. Now some merchants have added some fine stone powder to it, reducing the activity of mineral powder and affecting the strength of concrete.

1.2.1 Mineral powder warehousing. The storage of mineral powder is the same as that of cement, which is also unlocked by two departments at the same time. This also prevents the mineral powder from hitting the cement and fly ash tanks.

1.2.2 Mineral powder inspection. Mineral powder samples must also be registered in the warehousing account first, and then re inspected. For each batch of mineral powder, the activity index must be inspected.

1.3 Sand and stone

At present, the most difficult thing to control for concrete is sand and gravel. Because there are many sand and gravel producing areas and multiple suppliers, the quality of sand and gravel pulled is uneven. Below, the author discusses the quality control of sand and gravel. Before each truck of sand and gravel enters the factory, a quality inspector shall be arranged to conduct visual inspection. Vehicles with doubts in visual inspection shall not be unloaded first, and the mud content and mud lump content shall be tested first. Those tested beyond the national standard shall be returned. Those with needle and flakiness, crushing value and weathered sand content exceeding the standard shall be unloaded separately in the stock yard, and 30% shall be added when producing low strength concrete. In order to make money, some suppliers use wind fossils to break into sand to imitate river sand. This kind of sand has low crushing value, large water demand, and has a great impact on the workability and strength of concrete by absorbing additives. This kind of sand must not enter the factory. There are also some suppliers who mix rice stone, stone chips and ultra-fine sand into machine-made sand. Because the color is yellow, and some Grade III fly ash is added for coloring, they do not come during the day, but only come at night. It is difficult for the quality inspector to see clearly, so it is the most difficult to control the sand and stone. For these suppliers, the author assigned special personnel to take samples of each vehicle's sand on the night shift for water washing. After washing, the ingredients in the sand should be checked. Those found unqualified should be returned and replaced, and a warning should be given.

1.4 Admixtures

Admixtures are also very important raw materials in concrete, because they can reduce the water consumption of concrete, thus improving the strength of concrete. If the quality of admixture is unqualified, the water consumption of concrete will be increased, which greatly reduces the strength of concrete. In order to ensure the strength of concrete, it is required that after each vehicle of admixture is sampled, the test shall be carried out first, the water reduction rate shall meet the national standard, and the slump shall not be lost for 1h before warehousing, otherwise, it shall be returned.