CN105926656B - Construction Method of Mass Concrete Foundation - Google Patents

Abstract

The invention discloses a construction method of a large-volume concrete foundation, which is characterized in that the large-volume foundation is sequentially divided into four pouring areas at equal intervals from left to right, each pouring area is provided with a slow pouring area, the slow pouring area is provided on the right of the pouring area, concrete in the four pouring areas is poured respectively during construction, the concrete in each slow pouring area is poured after the concrete in each area is poured for 10-12 hours, the concrete in the slow pouring area adopts expansive concrete, concrete holes are formed in the large-volume foundation, fly ash is doped into the concrete to reduce the cement consumption, and the cement adopts slag cement with low hydration heat; the wood calcium water reducing agent is doped, after concrete is finally set by trowelling, compacting and pressing, plastic films and straw mats are adopted in time to cover the concrete, and then the concrete is watered and maintained for no less than 7 days.

Description

Construction Method of Mass Concrete Foundation

technical field

The invention relates to a construction method of a large-volume concrete foundation, which is suitable for the construction field.

Background technique

With the continuous emergence of modern high-rise buildings, mass concrete foundations appear from time to time in engineering construction. Due to the large amount of concrete in the mass concrete foundation, temperature stress will be generated during the concrete setting process. If there are no effective technical measures, the mass foundation will crack and other phenomena. It can be seen from the formation process of cracks that the cracking of concrete, especially mass concrete foundation, is mainly the result of the contradiction development between the tensile stress of concrete and the tensile strength of concrete foundation itself. Therefore, in order to control the cracks of the mass concrete foundation, it is necessary to improve the tensile strength performance of the concrete foundation itself and reduce the temperature stress as much as possible.

Contents of the invention

The invention provides a construction method for a large-volume concrete foundation and solves the problem of cracking of the large-volume concrete foundation.

The present invention alleviates the problem of temperature stress from four aspects. 1. Set holes inside the large-volume foundation to reduce the amount of concrete. After the holes are set inside the large-volume foundation, the bearing performance will not be greatly weakened. At the same time, the concrete material will have Larger savings; second, reduce temperature stress by setting the adjustment of concrete pouring method; third, reduce temperature stress through structural construction measures; reduce temperature stress through reasonable selection of materials.

According to computer simulation analysis, larger temperature stress bands will appear in the 1/4 to 1/3 area of the large-volume foundation. In the present invention, the large-volume foundation is divided into four pouring areas at equal distances from left to right. Each pouring area The slow pouring area is reserved, and the slow pouring area is left on the right side of the pouring area. The length of the slow pouring area is 600-800mm. During construction, the concrete in the four pouring areas is poured separately. The concrete in each slow pouring area is 10 ~ 12 hours before pouring, the concrete in each area will produce hydration reaction after pouring, resulting in higher temperature, the concrete that has been poured in each area will obtain the release of temperature stress in the slow pouring area, and each slow pouring The interim period between the regional concrete and the poured concrete in each area should be suitable to prevent the old and new concrete from being well connected in this position. The interim period of the present invention is obtained through a large number of experiments. The concrete in the slow pouring area adopts expansive concrete, and the strength of the expansive concrete is higher than that of the non-slow pouring area by one strength level, and a larger expansion stress is given to the section with a larger shrinkage stress. The concrete in the slow pouring area is mixed with a retarder, and the retarding time of the concrete in the slow pouring area is 4 hours longer than that of the poured concrete, so as to provide an adjacent side limit for the concrete in the slow pouring area, so that the stress generated inside the concrete can offset part of the tensile stress of the concrete, thereby Can reduce the appearance of cracks.

Bury tensile structural steel bars at the junction of the slow pouring area and the non-slow pouring area. The diameter of the tensile structural steel bars is 6-8mm, and the spacing of the tensile structural steel bars is 50-100mm. The tensile structural steel bars are uniform and symmetrical along the upper and lower layers of the section. configure. At the junction of the slow pouring area and the non-slow pouring area, the tensile stress of the concrete due to shrinkage or other reasons is borne by the tensile structural steel bars, which can effectively limit the expansion of cracks.

Radial ribs are placed at the corners of each area of the large-volume foundation. The diameter of the radial ribs is 14-18 mm. Due to temperature changes and concrete shrinkage, stress concentration will occur and cause cracks. Radial ribs can well avoid this phenomenon.

Linoleum is laid between the large-volume foundation and the concrete cushion below, and the linoleum not only acts as a waterproof layer, but also as a sliding layer. Due to the temperature shrinkage stress caused by constraints at the boundary, a sliding surface is set on the contact surface with the external constraints on the large-volume foundation, which can greatly weaken the external constraints, and the linoleum acts as a sliding layer.

Concrete holes are set inside the large-volume foundation, and the concrete holes are realized by air bladder inflation. The material of the bladder is rubber with a thickness of 5mm, so that it can withstand sufficient pressure. An air inlet nozzle is installed at one end of the skin bag, and a pressure gauge and a ball valve are installed, which is beneficial to control the gas pressure in the skin bag and control inflation. The skin bag should be preliminarily inflated before installation. The initial inflation pressure of the skin bag is 0.02MPa. After the skin bag is installed, the air pump is used to inflate again, so that the air pressure in the skin bag reaches the final pressure and the inflation is stopped, and then the pouring can be continued until completion. The final pressure of the bladder inflation is determined according to the diameter of the concrete hole. When the diameter of the concrete hole is less than or equal to 75mm, the final pressure of the bladder inflation is 0.04MPa; when the diameter of the concrete hole is greater than 75mm and less than or equal to 100mm, the final pressure of the bladder inflation is 0.05 MPa; when the diameter of the concrete hole is greater than 100mm and less than or equal to 125mm, the final pressure of airbag inflation shall be 0.06MPa; when the diameter of the concrete hole is greater than 125mm and less than or equal to 150mm, the final pressure of airbag inflation shall be 0.07MPa; When it is greater than 150mm, the final inflation pressure of the bladder is 0.08MPa. The surface of the leather bag is coated with new engine oil to facilitate demoulding.

After 12 hours of concrete pouring, the bladder can be deflated and drawn out. Because the bonding between the concrete and the rubber of the bladder and the air in the bladder cannot be released completely, the surface of the bladder is still mostly connected with the concrete, and it is difficult to extract it. A simple steel bar extractor is used for preliminary demoulding. The main rod of the steel bar extractor is two welded steel bars with a diameter of 25mm. The end of the steel bar is welded with an oval steel bar cage. The outside of the steel bar is wrapped with tape to prevent the steel bar or the welded joint of the steel bar from scratching the skin. Insert the steel bar capsule extractor into the joint between the skin capsule and the concrete, and insert it while shaking it slightly. After the skin is initially separated from the concrete, the skin can be extracted manually.

The amount of cement used in large-volume foundation concrete is not more than 350kg/m ³ , and fly ash is added to the concrete to reduce the amount of cement. The amount of fly ash added is 5% to 10% of the cement mass, and the cement uses slag with low heat of hydration Cement to reduce surface cracks or penetrating cracks in concrete elements.

The water consumption of the hydration reaction in concrete only needs 20% to 25%. If the water consumption is too much, after the water in the concrete evaporates, it will cause a large number of capillary pores in the concrete, and increase the shrinkage of the concrete, which will also affect its performance. Impermeability. In order to reduce water consumption and meet the pumpability and workability requirements of concrete, wood calcium water reducer is added, and the wood calcium water reducer is 0.25% of the cement dosage.

Coarse aggregate of concrete is crushed stone with a particle size of 5-40mm. The particle size of traditional coarse aggregate is 5-25mm. If the particle size is smaller to meet the design strength requirements of concrete, the amount of cement will increase, which will also increase the shrinkage of concrete.

The slump of traditional pumped concrete is too large, and the slump of pumped concrete is 14 to 16 cm. The pouring beams and slabs are only tamped with vibrating rods, and then the concrete is leveled with a wooden ruler. The plastic shrinkage of early concrete and the common quality problems of settlement shrinkage cracks. The invention properly reduces the slump of the concrete. The slump of the pumped concrete is 10-12 cm. Before the initial setting, the concrete is rubbed flat and compressed twice to avoid plastic shrinkage and settlement shrinkage cracks.

The formwork should not be removed prematurely, and the formwork should be removed after 7 days of concrete pouring. During maintenance, the wooden formwork should be fully watered to soak it, which can not only dissipate heat but also keep heat. Backfill the rammed earth at any time, so that the moisture in the soil can be used to continue curing the concrete to prevent cracks.

After the concrete is finally set with wooden mop under pressure, it shall be covered with plastic film and straw mat in time, and then watered for curing for no less than 7 days. After the concrete is poured, the heat of hydration makes the internal temperature reach a certain temperature. If the plastic film is not covered with straw mats for heat preservation, the internal temperature difference will cause the stress generated inside the concrete to exceed the limit and cause cracks on the concrete surface; , when the temperature drops sharply, the concrete will shrink, and the tensile stress produced by it, with the increase of the age of the concrete and the increase of the strength of the concrete itself, the constraints on the shrinkage stress of the cooling will become more and more large. If at this time Concrete is not strong enough to resist this shrinkage stress, and cracks can also develop. Cover with plastic film and grass mat and water for curing to ensure that the shrinkage of the concrete is small during the hardening process, and to avoid cracks caused by the overlapping of dehydration shrinkage and temperature drop peaks.

The invention has reliable quality and convenient operation.

Detailed ways

In this embodiment, the large-volume foundation is divided into four pouring areas at equal distances from left to right. Each pouring area is left with a slow pouring area, and the slow pouring area is left on the right side of the pouring area. The length of the slow pouring area is 600-800mm. During the construction, the concrete in the four pouring areas shall be poured separately, and the concrete in each slow pouring area shall be poured after 10 to 12 hours after the concrete pouring in each area is completed. The strength is increased by one strength level, and the concrete in the slow pouring area is mixed with a retarder, and the retarding time of the concrete in the slow pouring area is 4h longer than that of the poured concrete.

Bury tensile structural steel bars at the junction of the slow pouring area and the non-slow pouring area. The diameter of the tensile structural steel bars is 6-8mm, and the spacing of the tensile structural steel bars is 50-100mm. The tensile structural steel bars are uniform and symmetrical along the upper and lower layers of the section. configuration.

Radial ribs are placed at the corners of each area of the large-volume foundation, and the diameter of the radial ribs is 14-18mm.

Linoleum is laid between the mass foundation and the concrete cushion below.

Concrete holes are set inside the large-volume foundation, and the concrete holes are realized by inflating bladders, and the material of the bladders is 5mm thick rubber. An air inlet nozzle is installed at one end of the skin bag, and a pressure gauge and a ball valve are housed. The skin bag should be preliminarily inflated before installation. The initial inflation pressure of the skin bag is 0.02MPa. After the skin bag is installed, the air pump is used to inflate again, so that the air pressure in the skin bag reaches the final pressure and the inflation is stopped, and then the pouring can be continued until completion. The final pressure of the bladder inflation is determined according to the diameter of the concrete hole. When the diameter of the concrete hole is less than or equal to 75mm, the final pressure of the bladder inflation is 0.04MPa; when the diameter of the concrete hole is greater than 75mm and less than or equal to 100mm, the final pressure of the bladder inflation is 0.05 MPa; when the diameter of the concrete hole is greater than 100mm and less than or equal to 125mm, the final pressure of airbag inflation shall be 0.06MPa; when the diameter of the concrete hole is greater than 125mm and less than or equal to 150mm, the final pressure of airbag inflation shall be 0.07MPa; When it is greater than 150mm, the final inflation pressure of the bladder is 0.08MPa. Coat the surface of the leather bag with new engine oil.

After 12 hours of concrete pouring, the bladder can be deflated and drawn out. Because the bonding between the concrete and the rubber of the bladder and the air in the bladder cannot be released completely, the surface of the bladder is still mostly connected with the concrete, and it is difficult to extract it. A simple steel bar extractor is used for preliminary demoulding. The main rod of the steel bar extractor is two welded steel bars with a diameter of 25mm. The end of the steel bar is welded with an oval steel bar cage. The outside of the steel bar is wrapped with tape to prevent the steel bar or the welded joint of the steel bar from scratching the skin. Insert the steel bar capsule extractor into the joint between the skin capsule and the concrete, and insert it while shaking it slightly. After the skin is initially separated from the concrete, the skin can be extracted manually.

The amount of cement used in large-volume foundation concrete is not more than 350kg/m ³ , and fly ash is added to the concrete to reduce the amount of cement. The amount of fly ash added is 5% to 10% of the cement mass, and the cement uses slag with low heat of hydration cement.

Add wood calcium water reducer, wood calcium water reducer is 0.25% of cement dosage. Coarse aggregate of concrete is crushed stone with a particle size of 5-40mm. The slump of the pumped concrete should be 10-12cm. Before the initial setting, rub it flat and compress it twice with a wooden mop to avoid plastic shrinkage and settlement shrinkage cracks.

Formwork removal should be carried out after 7 days of concrete pouring. During maintenance, it should be fully watered to soak the wooden formwork, which can not only dissipate heat but also keep heat.

After the concrete is finally set with wooden mop under pressure, it shall be covered with plastic film and straw mat in time, and then watered for curing for no less than 7 days.

Claims (1)

1. A construction method for a mass concrete foundation, characterized in that the mass foundation is divided into four pouring areas equidistantly from left to right, each pouring area is left with a slow pouring area, and the slow pouring area is left on the right side of the pouring area , the length of the slow pouring area is 600-800mm. During the construction, the concrete in the four pouring areas is poured separately. The concrete in each slow pouring area is poured after 10 to 12 hours after the concrete pouring in each area. The concrete in the slow pouring area uses expansion Concrete, the strength of expansive concrete is higher than that of non-slow pouring area by one strength grade. The concrete in slow pouring area is mixed with retarder, and the retarding time of concrete in slow pouring area is 4h longer than that of poured concrete; concrete holes are set inside the large-volume foundation; The amount of cement used in large-volume foundation concrete is not more than 350kg/m ³ , and fly ash is added to the concrete to reduce the amount of cement. The amount of fly ash added is 5% to 10% of the cement mass, and the cement uses slag with low heat of hydration Cement; mixed with wood calcium water reducer, wood calcium water reducer is 0.25% of the amount of cement; concrete coarse aggregate uses crushed stone with a particle size of 5-40mm; After covering with film and grass mat, watering and curing shall not be less than 7 days.