influence of cement dosage
The stable section volume of everyday portland cement increases for the duration of hydration and hardening, while the cement + water system shrinks. Secondly, the cement hydration technique is accompanied by thermal outcomes, which motive the initial quantity to enlarge and decrease when cooling, ensuing in an increase in apparent shrinkage. Besides, there is also a phenomenon of self-shrinkage because of self-absorption at some stage in cement hydration. Therefore, in preferred, if different conditions are identical, the amount of cement will increase growth, and the shrinkage of froth concrete will affect growth accordingly. At an identical time, cement is one of the critical factors to make sure electricity, so there may be an appropriate variety of cement dosage.
The effect of cement kinds
No longer all the quantity of cement earlier than and after hardening shrinks. The extent of increased cement no longer simplest shrinks but also swells earlier than and after hardening. Consequently, if the ideal quantity of enlargement cement is used, the overall shrinkage of the foamed concrete can be compensated or reduced to a sure extent. But, the expansion cement not handiest influences the volume trade but additionally influences a chain of other residences. If it’s far an excessive amount of, it’s going to cause the shape of the hardened foam concrete to be damaged. Therefore, the type and dosage of the expansion cement need to be determined via experiments.
The impact of aggregate
Experimental and engineering records show that the shrinkage of ordinary cement concrete is the smallest, the shrinkage of cement paste is huge, and the shrinkage of foam concrete is the most important. That is due to the fact regular concrete is blended with a huge amount of coarse mixture with a consistent extent, and the total extent of cement paste without aggregate is reduced before and after hardening. The largest shrinkage of froth concrete is, on the one hand, because there may be no coarse aggregate therein, and on the other hand, because it contains a large number of pores, most of the gaps are filled with water. For the duration of use, as the water inside the pores evaporates, the arrival indicates a quantity shrinkage. It may be visible that the addition of combination is surely one of the measures to reduce the shrinkage of foamed concrete, and foamed concrete can best be combined with a part of the excellent mixture. On the identical time, due to the fact, the combination is chemically inert, excessive addition will result in a vast decrease inside the power of the foamed concrete, and hence its amount may be constrained. After the foam concrete’s density, water-cement ratio, and other manner parameters are decided, the pleasant mixture will boom, and the quantity of cement will lower. Consequently, there may be additionally an appropriate preference of whether the aggregate is blended or now not.
impact of water-cement ratio and conservation machine
The moisture loss and drying shrinkage check results of froth concrete at 60℃show that there may be a clear and near synchronization among water escape and shrinkage change of hardened foam concrete. This suggests that the break out of moisture directly causes the shrinkage of the foam concrete, and while the moisture stops escaping, the froth concrete stops shrinking. Consistent with conventional cement chemistry theory, the quantity of water required for complete cement hydration; this is, the theoretical water-cement ratio has to be zero.38. In evaluation, the foamed concrete’s molding water-cement ratio is frequently as excessive as 0.7 or even 0.eight. Excess water will remain inside the pores of the hardened foam concrete, and this part of the water will account for about half of the quantity of molding water. Once the encircling relative humidity is low, or the ambient temperature is excessive, the moisture evaporates and then escapes. Especially within the early stage of hardening, the structure of foamed concrete is still pretty vulnerable. If it isn’t well maintained, moisture is easily lost, leading to big shrinkage and floor cracking, weakening the inner shape of the hardened frame, and triggering high water absorption of the hardened foamed concrete. In line with this, the initial water-cement ratio of foamed concrete will become a prerequisite element affecting the shrinkage of hardened foamed concrete. One of the key technologies for making ready low-cut back foam concrete is to govern the low water-cement ratio. After pouring the foam concrete pattern with a density of 1100 kg/m3 for twenty-four hours, it became divided into two batches of samples with a surface nylon film sealed and no floor dealt with. The samples were cured inside the equal environment, like temperature and humidity. Dry shrinkage. Thru evaluation, it’s miles recognized that the shrinkage of the pattern after the floor sealing treatment is a great deal smaller than that of the sample with an open floor, and the shrinkage has a tendency to be stable at the age of 5 days. The consequences another time proved the close relationship among water break out and shrinkage and the importance of early water retention to control foam concrete shrinkage.
Technical measures to lessen shrinkage and cracking of foamed concrete
according to the above analysis, the technical measures to lessen the shrinkage of foamed concrete and prevent cracking and water absorption specifically consist of the following elements:
(1) the suitable amount of cement;
(2) including the perfect quantity of expansion cement;
(3) Low molding water-cement ratio;
(4) Optimize the conservation system and improve early water retention;
(5) using waterproofing marketers (combined or surface coating);
(6) add barbed twine (crack prevention net) to the insulation layer to prevent the cracking of the foam concrete.
By optimizing the concrete mix ratio and controlling construction measures, early cracking of the concrete can be reduced.