Qin Haijuan nodded and said: "You remember, the slump of the concrete mixture is measured in millimeters, the measurement accuracy is 1mm, and the result is expressed to 5mm. In addition, the apparent density test of concrete, the instruments and equipment used include a volumetric cylinder, which is a cylinder made of metal with handles on both sides. For the mixture with a maximum particle size of aggregate not more than 40 mm, a volumetric cylinder with a volume of 5 liters is adopted, and its inner diameter and cylinder height are both 186±2 mm, and the wall thickness of the cylinder is 3 mm; when the aggregate particle size is greater than 40 mm, the inner diameter and cylinder height of the volumetric cylinder should be greater than 4 times of the maximum particle size of aggregate. There is also a bench scale, which weighs 100kg and has an inductance of 50 grams. The frequency of the shaking table should be 50±3Hz, and the amplitude should be 0.5±0.1 mm when no load is used. Trumpet, steel rod with a diameter of 16 mm and a length of 600 mm, the ends should be rounded. These will be taken in the future when you take the tester induction certificate exam, so you should also keep it in mind. ”

"Okay, let's talk about the practical steps, the first step is to wipe the inside and outside of the volumetric cylinder with a damp cloth, and weigh the cylinder, accurate to 50 grams. The second step is that the charging and tamping method of concrete should be determined according to the consistency of the mixture. For concrete with a slump of no more than 70 mm, it is advisable to use a vibrating table to vibrate it, and it is advisable to use a tamper for more than 70 mm. The third step is to scrape off the excess concrete mixture with a scraper, and if there is a depression on the surface, it should be filled. Wipe the outer wall of the volumetric cylinder and weigh out the total weight of the concrete and the volumetric cylinder, accurate to 50 grams. Finally, the result is calculated, and the result should be accurate to 10kg/m3, which needs to be noted. Okay, you can start measuring. ”

The apparent density test of concrete is a fairly simple test, and the apparent density is soon measured to be 2360kg/m3, which is also within a reasonable range from the design apparent density of 2350kg/m3, so it can be concluded that the performance of the concrete mixture basically meets the requirements.

The next step is to do an air content test, which is equivalent to a verification of the apparent density.

Qin Haijuan also said: "The following is used for gas content testing, and the instruments and equipment needed are pneumatic gas content tester tamper or vibrating table, and there is also a platform scale weighing 100 kilograms and a sensing weight of 50 grams. ”

The three testers quickly brought the corresponding instruments and equipment to prepare for the test.

Qin Haijuan continued: "Let me talk about the test steps, first of all, we must determine the gas content in the aggregate. This measurement method is like this, first calculate the weight of coarse and fine aggregates in each sample according to the formula, the second step is to fill one-third of the height of water in the container, mix the weighed coarse and fine aggregates, and slowly pour them into the container, and the water surface should be gently inserted and pounded 10 times every 25 mm or so, and stirred slightly to exclude the air that is mixed in. During the feeding process, the liquid level should always be kept high on the top surface of the discharge, after all the aggregate is added, soak for another 5 minutes, and tap the outer wall of the container to remove air bubbles, then remove the foam on the water surface, add water to full, and wipe the edge of the container. ”

Li Liangfeng took the two newcomers and began to operate according to the steps Qin Haijuan said, and at this time, Qin Haijuan also slowly explained: "Okay, after these two steps are done, put the sealing ring, cover and tighten the bolts, and close the operation valve and exhaust valve." Open the intake valve and pump up with a pump. Make the pressure in the air chamber slightly greater than 0.1MPa, and tap the dial to make the hands steady. Open the exhaust valve and adjust the pressure with the operating valve so that the pointer of the pressure gauge is just at 0.1MPa. Then close all valves tightly. Open the operating valve to let the compressed air in the air chamber enter the container, and after the pressure gauge pointer is stable, the gauge value is read. In this way, the gas content value of the aggregate is found according to the relationship curve between pressure and air content, which should be accurate to 0.1%. ”

In fact, these tests are relatively simple, as long as they are carried out in accordance with the prescribed method, so the gas content of the aggregate can be measured quickly.

Qin Haijuan continued: "Now that the gas content of the aggregate is measured to be 1.6, then the air content of the concrete will be measured next. Wipe the inner surface of the container and lid with a damp cloth first, and then load the concrete specimen for tamping. The second step is tamping, which is divided into two forms: mechanical vibration and manual tamping. Concrete with a slump of no more than 70 mm should be compacted with a vibrating table, and tamping with a tamper when it is more than 70 mm. It should be noted that when the concrete quality inspection is carried out at the construction site, the tamping method should be carried out according to the tamping method actually adopted during construction. Of course, we are not on-site, so we still use manual methods. After tamping, it should be scraped with a scraper immediately, and if there is a depression on the surface, it should be filled, and then smoothed with a spatula to make the surface smooth. If the bulk density of concrete needs to be determined at the same time, it can be calculated at this time. Then paste a small piece of plastic film on the concrete surface facing the operating valve hole, wipe the edge of the upper mouth of the container, place the sealing ring, cover and tighten the bolts. Then the fifth step is to close the operating valve, open the intake valve, pump up the air with a cylinder, make the pressure in the empty chamber slightly greater than 0.1 megapascals, lightly buckle the dial to make the pointer stable, open the exhaust valve, and adjust the pressure with the operating valve so that the needle of the manometer is just 0.1 megapascals, and then close all the valves. Open the operating valve, let the compressed air in the air enter the container, and after the pressure gauge pointer is stable, the gauge value is measured. Finally, open the vent valve, relieve the pressure, and repeat the procedure to take another meter reading of the specimen that has been loaded into the container. ”

After Li Liangfeng and the others finished, Qin Haijuan said again: "Based on the average value of the two measurements, find out the corresponding gas content value according to the relationship curve between the gas content and the pressure gauge reading. If the difference between the two measurements is greater than 0.2%, the third measurement should be performed, and if the correlation between the third measurement result and the closest value of the previous two measurements is still greater than 0.2%, then the real yàn is invalid. It seems that the test error is not large, just right, one 4.6, one 4.4, then the average is 4.5. It's not over yet, you need to subtract the aggregate gas content with this result, so that it is the air content of the concrete. ”

The results showed that the concrete had an air content of 2.9, which met the requirements of the code. The air content of concrete is also a very important indicator, high air content can improve the working performance of concrete on a certain degree, but if it is too high, it will affect the strength of concrete, so it must be within an acceptable range.

Qin Haijuan said again: "I'll talk about the verification of the container volume. Weigh the total weight of the drying container and glass plate to an accuracy of 50g, and add water to the container close to the upper edge. Then push the plate with water to cover the mouth of the container and make it free of any air bubbles under the glass. Wipe off the remaining water on the outside of the container and the upper glass plate, and weigh to an accuracy of 50 grams. The difference between two weighings is the volume of the container. Carefully remove the glass pane to avoid bringing moisture out. There is also the calibration of the instrument. After the container is filled with water, put the sealing ring and cover and tighten the screw bolt, close the operating valve, open the air intake valve, measure the instrument value when the air content is 0% according to the actual yàn step, open the exhaust valve, relieve the pressure, open the lid and suck out the water equal to 1% of the volume of the container, cover and tighten the bolts, repeat the above steps to read the reading value of the pressure gauge with an air content of 1%. Continue to measure the pressure gauge readings when the gas content is 2%, 3%, 4%, 5%, 6%, 7%, and 8% according to the above method. Each of these readings should be accurate to 0.001 megapascals. Based on the measurement results, the relationship between the gas content and the pressure gauge reading is plotted. The relationship between the change in the total volume of gas in the instrument and the gauge pressure value should be in accordance with Boyle's law. If there is a significant deviation, it should be re-calibrated. (To be continued.) )