【Daily Topic】【Engineering Version 20160522】

Methods to improve the final strength of concrete include (　ABCD　). 　　A. Increase the cement strength grade B. Increase the water-cement ratio C. Improve mixing and vibration compaction D. Raise the curing temperature of the concrete E. Use pozzolanic cement

　　(1) Use cement of high strength grade. Increasing the strength grade of cement can effectively enhance the strength of concrete. However, since an increase in cement strength is limited by raw materials and production processes, relying solely on raising cement strength to improve concrete strength is often impractical and uneconomical. 　　(2) Reducing the water-cement ratio This is an effective measure to improve concrete strength. Reducing the water-cement ratio of the concrete mixture can lower the porosity of the hardened concrete, significantly enhance the bond between cement and aggregates, and thereby increase its strength. However, reducing the water-cement ratio will decrease the workability of the concrete mixture. Therefore, corresponding technical measures must be employed, such as using mechanical force for vibration or adding admixtures to improve workability. 　　(3) Moist-heat curing In addition to techniques such as steam curing, autoclave curing, and preheating of aggregates in winter, the hydration heat stored within the cement itself can also be utilized to increase the rate of strength development. 　　(4) Age adjustment As mentioned earlier, the strength of concrete continues to increase as it ages. Practice has shown that when the age of concrete is between 3 and 6 months, its strength increases by 25–50% compared to that at 28 days. For concrete in certain parts of a structure that can only be put under load after 6 months, the strength grade of that concrete can be appropriately reduced to save cement. However, in practical application, it must be approved by the design and management authorities. 　　(5) Improving construction techniques 　　Methods such as mechanical mixing and vigorous vibration can help to ensure that the concrete mixture is poured more evenly and compactly even at low water-cement ratios, thereby achieving higher strength. In recent years, new construction methods developed abroad such as high-speed mixing method, secondary feeding mixing method, and high-frequency vibration method have been applied in domestic projects, achieving good results. 　　(6) Addition of admixtures Adding admixtures is one of the effective methods for improving concrete strength; both water reducers and early-strength agents have a significant impact on the development of concrete strength.

A. Increase the cement strength grade C. Improve mixing and vibration compaction

AC~~~~~~~~~~~~~