混凝土原材料与施工缝处理

选用水泥应根据混凝土设计要求而定；掺加I级或Ⅱ级粉煤友，可以改善混凝土性能、节约水泥和减少水泥水化热；混凝土中必须掺加适量外加剂，同样可以改善混凝土性能和减少用水量等；对水泥、骨料、掺合剂和外加剂都必须控制合碱量，可以提高混凝土的耐久性和防裂能力。为简化混凝土施工程序和适应大型施工机械化的需要，研究和采用混凝土施工缝不打砂浆，取而代之的是施工缝面第一层浇筑二级配混凝土或三级配富浆温凝土。从国内外试验和工程实践看，不打砂浆在技术上是可行的，但必须精心组织和精心施工。混凝土施工缝面的处理标准是：去掉乳皮，微露粗砂，表面粗糙。用25—50MPa高压水冲毛的施工缝面质量可靠并可取得明显的经济效益。

Concrete raw materials and treatment of construction joints

The hydraulic concrete construction technology incorporates a series of disciplines and involves technical fields. In this paper the concrete raw materials and how to treat construction joints are summarized. The cement shall be singled out according to the concrete design. Addition of fly ash type I or II can refine the properties, cut down the cement content and cement hydration. The concrete shall be added with certain additives that can also improve concrete behaviour and reduce cement content. The alkali shall be controlled in cement, aggregates, admixtures and additives in order to enhance the durability and anti-cracking of concrete. To simplify construction procedures and meet the need for mechanized construction by heavy equipment, it is considered necessary that concrete construction joint with directly laying of two-gradation concrete or three-gradation rich concrete rather than with mortar is studied and applied. Based on experiments and engineering practice at home and abroad, the construction joint technology without mortar is practicable, but the construction shall be elaborately and carefully carried out. The treatment criteria include scaling off of the laitance and outcropping of coarse sand, finally exhibiting rough surface. A high quality construction joint and significant cost-benefit can be obtained by roughening with water jet of 25-50 MPa.