您的位置:首页 > 女性

建筑工程裂缝绝大数是由这些因素导致的

时间:2019-07-15
诚博娱乐官网

影响结构裂缝的主要因素有:温差或收缩率,线膨胀系数,弹性模量,厚度或壁高,基础与结构的约束程度,结构长度,材料成分和物理力学性能,以及施工过程和环境影响。

大约80%的施工裂缝是由上述因素引起的。

原因一:材料失效导致裂纹

(1)不合格水泥或水泥品种使用不当造成的裂缝

1.原因分析:

(1)使用稳定性不理想的水泥,在水化后固化和硬化水泥的过程中,在有害物质的作用下,发生剧烈的不均匀体积变化,在构件内部产生破坏性应力,导致混凝土减少强度。开裂;

(2)不同品种,不同等级水泥的性能完全不同。水化后初凝和最终凝固的时间不同,收缩率也不同,引起开裂;

(3)施工人员不完全了解水泥的性质或工程性质,滥用水泥,未采取相应的技术措施,造成损坏或裂缝。

2.控制措施:

(1)当强度等级低于设计要求且裂缝宽度大于0.3 mm时,需要重新加工;

(2)经检验,部件的混凝土强度等级达到设计要求,当裂缝宽度小于0.3mm时,可通过化学灌浆封闭裂缝。

(2)砂石混合料中的泥浆含量超标,细砂或混合料选择不当造成组分裂纹

1.原因分析:

(1)使用劣质产品,加入后不起作用,直接影响组件质量,导致混凝土强度下降,出现裂缝;

(2) The mud content of the aggregate is not controlled strictly. The clay, dust and organic impurities attached to the aggregate surface affect the cement cementation, so that the mud floats on the surface layer of the component. When the concrete component is hardened, the mesh shrinkage crack is generated.

(3) The matching ratio is inaccurate, causing the dosage of the admixture to be too large, so that the concrete mixture cannot be hardened, causing damage to the concrete member.

2. Control measures:

(1) When the concrete strength level of the tested component is lower than the design requirement, the relevant department must study the reinforcement treatment plan;

(2) When causing cracks in the component, the strength of the concrete of the component should be checked first. If the design requirements can be met, the cracks can be closed by chemical grouting according to the actual width, length and position of the cracks to restore the original function and prevent corrosion of the steel.

Reason 2: Cracks in concrete members caused by the template system

(1) Cracks generated by the irregularity of the template support

4c6fc83fc3674c35abcb08c601f8e602

1. Reason analysis:

(1) Before the template is supported, the size and spacing of the material of the bracket are not calculated according to the engineering structure and the size of the upper load. The blind estimation is determined, resulting in deformation of the bearing capacity and rigidity during construction, resulting in cracks in the newly poured concrete. Serious collapses will occur;

(2) Improper construction management. Before the foundation template is supported, the foundation soil and the laying cushion are not smashed first, and the base soil does not reach the standard of the bearing layer; or the soil is hard and dry, in the process of concrete pouring, the foundation soil is softened by watering, seeping and damping, The stent is settling and deformed under the pressure of the upper load, causing cracks in the concrete member.

2. Control measures:

(1) Check the actual condition of the deformed member. If the maximum bending deformation of the beam and the plate is less than 20mm, it can be left untreated, and only the appearance should be corrected when plastering;

xx(2) Check the width of the upper crack of the component, timely use the grout to compact the compaction, and strengthen the wet curing.

(2) Cracks caused by the formwork stand standing on the floor

1. Reason analysis:

(1) During the construction of multi-storey buildings, the columns of the upper formwork are supported on the reinforced concrete floor slab newly poured on the lower floor, causing deformation and cracks in the floor. The width of the crack is narrow at the bottom and the top of the floor; the crack is more in the middle and less in the four sides;

(2) If the bottom mold and support of the new cast reinforced concrete floor slab have been removed, deformation and cracks will occur when the construction load of the upper stencil, bracket and cast concrete is greater than the bending compressive strength of the slab;

(3) Some construction speeds are relatively fast, and the concrete strength of the new concrete floor slab below has not reached the design value. Because the supporting columns of the upper and lower slabs are not aligned, under the action of the upper concentrated load, the slab is partially deformed and crack.

2. Prevention measures:

(1) Check the cracks in the floor and immediately add support for reinforcement to prevent the floor from continuing to deform and the cracks to expand;

(2) Check the crack width. When the crack width is less than 0.2mm and the bending deformation is less than 1/1000 of the span length, grouting can be used to restore the original function and prevent steel corrosion;

(3) When the crack width is greater than 0.3mm, the observation must be strengthened, and relevant personnel should be asked to study the reinforcement scheme.

(3) Cracks in the components caused by the early removal of the bottom mold and the bracket

1. Reason analysis:

(1) Demolition of the load-bearing beam and the bottom mold in advance, resulting in insufficient bearing capacity and deformation and cracks;

(2) Remove the cantilever beam and the cantilever plate bottom mold in advance, causing the concrete members to tip over, break and crack;

(3) If there is no anti-overturned brickwork or load on the upper part of the anchoring end of the cantilevered member, when the bottom mold and the bracket are removed, the overhanging member may be overturned;

xx(4)如果冬季施工温度低,如果使用的水泥种类不合适,如矿渣硅酸盐水泥或火山灰硅酸盐水泥制备混凝土,混凝土的强度会缓慢增加;但是,该站点仍然按照常规时间移除底部模具。由于构件的强度不足,支架引起变形和裂缝。在严重的情况下,会出现断裂或坍塌。

2.控制措施:

(1)检查裂缝宽度。当裂缝宽度小于0.2mm且弯曲变形小于跨度长度的1/1000时,采用灌浆封闭;

(2)当裂缝宽度大于0.3mm时,有必要加强观察,并邀请相关人员及时研究加固处理方案。

原因三:钢筋不规则施工引起的构件裂缝

(1)悬臂构件钢的不对中和下沉引起的裂缝和裂缝

2f641854637a40bebe42c439e90450e9

1.原因分析:

(1)悬臂构件在嵌入式支撑件处受到负弯曲距离(上部张力和下部压力),其与简单支撑梁结构的力相反。悬臂结构的受应力钢筋应位于上部。如果错误的主肋倒置,会导致事故;

(2)操作不规范。例如,当浇注悬臂梁和板的混凝土时,没有设置操作平台板,但是钢板表面上的钢板是踩踏的,而采摘梁上部的主肋是经常下台导致裂缝或断裂;/P>

(3)施工单元对悬臂结构不够重视,主肋直径错误或主肋反转,或者下沉位移值大,削弱了悬臂结构的承载力,或者混凝土强度等级为低于设计要求,过早移除模具,导致悬臂构件沿嵌入端的根部破裂和断裂。

2.控制措施:

检查已经破裂的悬臂梁中钢筋的直径,等级和数量。如果直径,数量和位置与设计不符,必须及时更换,以更换合格的钢筋。

(2)现浇楼板不规则弯曲引起的裂缝

1.原因分析:

(1)现浇板或附加结构肋的负弯曲距离泄漏,踩踏,下沉等,沿负弯曲区引起板的裂缝;

(2)悬臂板的附加肋条泄漏或放置较少,导致板角处出现斜裂纹;

(3)施工前,平衡不明确,板的负弯曲距离加固或附加结构肋条未得到重视。没有采取有效的技术措施来确保钢筋的顶部位置。

2.控制措施:

(1)对于浇筑的混凝土板,如果有裂缝,缝宽大于0.3mm,应查明相关人员的原因,并采取加固措施;

(2)如果负弯曲距离钢筋较少放置或下沉,则应采取加固和加固措施。

原因四:混凝土裂缝

(1)混凝土塑性收缩裂缝

干缩裂纹:当浇筑的混凝土仍处于塑性状态时,由于热风和风,水蒸发过快,出水率低于表面蒸发速率,导致构件表面水分流失过多开裂。裂缝是纵横交错的,没有规律性,沿着短的方向沿着板分布。随着时间的延长,裂缝发展到混凝土内部;裂缝是间歇性的,如连续不连续,有时是龟形,这种裂缝一般都是厚而短的,裂缝直到钢筋。

1.原因分析:

(1)使用收缩率大的水泥;或者使用更多的水泥,多用水,现场加水或混合物影响,如氯化钙,往往会增加混凝土的收缩值;

(2)对于体积和表比小的部件,混凝土中的水分容易蒸发,部件容易收缩;

(3)新浇混凝土的覆盖,挡风玻璃和湿养是不及时的。当风速从无风到六风时,混凝土中的水分蒸发量增加3倍,空气中的湿度从90%下降到50%,水蒸发速率增加5倍;环境温度从10°C升至20°C。水分蒸发量增加1倍;

(4)高温,干燥,强风等使混凝土失水过快,失水率大于混凝土出水速度。在塑性混凝土的表面收缩和内部约束下,弱硬结的拉伸表面会产生拉应力,产生不同长度的裂缝。

2.预防措施:

使用钢丝刷或平面研磨机去除水泥结膜并进行纹理化,扫掠和冲洗,并干燥。用聚合物砂浆修复整平。

(2)大体积混凝土温差裂缝

大体积混凝土:结构截面的最小尺寸在800mm以上,水化热引起的混凝土最高温度与环境温度之差预计超过25°C。对于大体积混凝土构件,在硬化期间,水泥的水化热高,构件的厚度大,内部温度不易分散,并且部件的外观随着自然温度而降低。当内部和外部之间的温差大于25℃时,表面产生冷缩应力。当应力大于此时混凝土的抗拉强度时,经常发生穿透构件的裂缝或不同深度的裂缝。

1.原因分析:

(1)混凝土流动性大,坍落度大,耗水量大,水泥用量大,砂磨率大,水泥水化热大。浇注速度快,大体积混凝土内外温差大,表面散热快,收缩大,产生裂纹;

(2)大体积混凝土中水泥使用不当。当水泥中硅酸三钙(Ca3Si)含量高达5.5%时,每千克水泥的热值为377kJ,比同等级矿渣水泥的热值高42kJ。组件的温差比要求大11%左右,更容易发生温差裂纹;

(3)为了满足混凝土设计强度的要求,往往需要增加混合比中的水泥用量,增加水泥标签,这两者都会产生高水化热。当施工环境的温度下降时,不采取有效的技术措施,并产生裂缝。

2.预防措施:

(1)大体积混凝土温度控制指标不应大于以下数值:

1大体积混凝土的浇注模温度控制在28°C以内。在夏季高温施工期间,应采取降温措施控制混凝土温度不超过28°C;

2注入模具后,大体积混凝土的最高温升为35°C。必要时,可采用人工冷却方法将冷却水管嵌入混凝土,循环水以降低混凝土内部温度;

3砼铸造构件内外温差应控制在25°C以内。

(2)浇注大体积混凝土时必须采取以下技术措施:

1使用低水化热水泥,如矿渣硅酸盐水泥,粉煤灰硅酸盐水泥。也可以考虑将粉煤灰和其他外加剂掺入普通硅酸盐水泥中,以减少水泥水化的热量;

2选择合理的砂石分级,严格控制泥浆含量不应超过1.0%;

3在混凝土中加入一定的混合物,以减少水泥的用量。经设计单位同意,混凝土的后期强度为60 d,可作为混凝土的强度评价。

(3)裂缝处理措施:

1观察裂缝稳定后,首先清洗裂缝,用加压水冲洗干燥;

2采用灌浆封闭处理,将裂缝混凝土结合成一个整体,恢复原有功能。

日期归档
  • 友情链接:
  • 诚博官网 版权所有© www.freeviagraa2gen.com 技术支持:诚博官网| 网站地图