C40-level extra-thick mass concrete pouring, in order to avoid harmful structural cracks in concrete, in the raw material selection and mix design, supply and pouring of concrete, concrete surface, the internal temperature detection and maintenance, etc. have taken effective measures.

Chien-fu Plaza is located in Fuzhou, Fuzhou Gutian Road. Building essentially square planar. On the ground 28 floors and 2 underground levels. Situ outside the box for the whole tube structure. The basis of the total floor area of approximately 2300m2 (49.2 × 47.8), the total amount of concrete is about 3900m3. The whole basis of the core barrel from the inside region of a large slab (about 600m2), around the many small caps and the caps formed between the bottom. Thick concrete floor 0.6m, thick concrete slab at 2.5m, concrete design strength grade C40.

Foundation slab of concrete, high strength, thickness and volume of large construction at the time of the cold spring, highlighting the difficulty is as follows:

To reduce the maximum temperature of mass concrete and control concrete within the temperature difference inside and outside the specified limits (25 ℃) within the existing three extremely adverse factors: ① floor (slab) concrete extra-thick, to a one-time pouring concrete internal temperature is not easy dissemination; ② high-strength grade of concrete, the general need to use silicon or silicon 425 of cement 525, the high heat of hydration; ③ spring construction, environmental temperature is low, concrete, large temperature difference between inside the table. Under the combined effect of these factors, the concrete house will inevitably lead to a higher temperature, there is the danger of cracks. In order to prevent cracking of concrete (surface cracks and through cracks), we must begin to reduce stress and improve the concrete temperature tensile properties of concrete itself, both comprehensive consideration. To this end, we have developed a relatively complete construction programs.

1.C40 mass concrete mix design and test with.

C40 mass concrete in order to reduce the maximum temperature, the most important measure is to reduce the hydration heat of concrete. Therefore, we must do a good job of concrete mix design and test with the work.

1.1. Raw material use.

1.1.1. Cement: C40 mass concrete should use a lower heat of hydration of cement, and to minimize the amount of cement. Selected this project 525 Lianshi cement.

1.1.2. Fine Aggregate: Sand should adopt Ⅱ area, because the use of sand than with fine sand, can reduce the amount of water and cement.

1.1.3. Coarse Aggregate: Among the pumping case, the choice of particle size 5-20mm continuously graded gravel to reduce the shrinkage deformation of concrete.

1.1.4. Clay content: In the large volume of concrete, the thickness of the aggregate containing mud volume is the crucial issue, if the aggregate amount of clay-containing ones, not only increased the shrinkage deformation of concrete, but also severely reduces the resistance of concrete tensile strength, the great danger of cracking. Therefore, aggregate sample must be on-site measurement, gravel containing mud volume control within 1%, sand containing mud volume control within 2%.

1.1.5. Admixture: application to add fly ash technology. In concrete mixed with fly ash can not only save cement, reduce heat of hydration and increase concrete workability, and can significantly improve the late strength of concrete, and the 28-day strength of concrete can basically close to the standard of concrete strength values. Therefore, this project uses 60 days of age of the concrete strength to strength instead of 28 days of age, control temperature rise rate, peak temperature rise occurs over time.

1.1.6. Admixtures: Using external UEA technology. In concrete to add about 10% of the UEA. Tests showed the concrete added the UEA, the concrete internally generated stress can be partially offset by the expansion of concrete shrinkage stress, so that a corresponding increase in anti-cracking strength of concrete.

1.2. Test with and construction of the mix to determine:

According to laboratory mix design, each 525 cubic meters of concrete mix proportion of cement No. 400kg, a continuous graded gravel (particle size 5-20mm) 1060kg, admixture 73kg, admixtures 6kg, water, 170kg, Slump 160 -- 180mm.