毕 业 设 计（论 文）外 文 参 考 资 料 及 译 文
译文题目：
学生姓名： 学 号：
专 业：
所在学院： 龙蟠学院
指导教师： 杜杨
职 称： 讲师
2011年 月 日
THE CRACK OF CONCRETE 1 cracks
Concrete cracks for many reasons, mainly temperature and humidity changes, the brittleness of concrete and uneven, as well as unreasonable structure, failure of raw materials (such as alkali-aggregate reaction), template deformation, differential settlement of foundation.
The concrete to harden during the evolution of considerable heat of hydration of cement, the internal temperature rising, the surface tension caused by stress. Late in the cooling process, due to coagulation on the basis of the constraints or old, will occur within the tensile stress in the concrete. Lower temperature in the concrete surface will cause a lot of tensile stress. When the tensile stress beyond the capacity of concrete cracking, the cracks will appear. Many of the internal humidity of concrete with little or changes slowly, but the surface may change more or humidity change dramatically. Such as conservation, failed to
Concrete cracks for many reasons, mainly temperature and humidity changes, the brittleness of concrete and uneven, as well as unreasonable structure, failure of raw materials (such as alkali-aggregate reaction), template deformation, differential settlement of foundation.
The concrete to harden during the evolution of considerable heat of hydration of cement, the internal temperature rising, the surface tension caused by stress. Late in the cooling process, due to coagulation on the basis of the constraints or old, will occur within the tensile stress in the concrete. Lower temperature in the concrete surface will cause a lot of tensile stress. When the tensile stress beyond the capacity of concrete cracking, the cracks will appear. Many of the internal humidity of concrete with little or changes slowly, but the surface may change more or humidity change dramatically. Such as conservation, failed to
keep dry when wet, the surface of concrete shrinkage deformation by internal constraints, but also often leads to cracks. Concrete is a brittle material, tensile strength is the compressive strength of about 1 / 10, short-term ultimate tensile deformation during loading only (0.6 ~ 1.0) × 104, the limit position when the long-term loading elongation only ( 1.2 ~ 2.0) × 104. the material is uneven, unstable water-cement ratio, and transport and Segregation in the pouring process, in the same piece of concrete in the tensile strength is uneven, there are a lot of tensile strength low, easy-to-weak parts of the cracks. In reinforced concrete, the tensile stress is mainly borne by the reinforced concrete is under stress. In plain concrete or reinforced concrete on the edges if the tensile stress within the structure there shall be to rely on concrete to bear. General design requirements in both the tensile stress does not appear or appear only very small tensile stress. However, the maximum temperature of concrete in construction to the operation of the cooling period of steady temperature, often caused by a large concrete internal tensile stress. Sometimes more than other things, thermal stress can be caused by stress loading, the variation of thermal stress control for the rational design and construction is extremely important.
2 Analysis of Thermal Stress
According to the formation of thermal stress can be divided into the following three stages:
(1) Early: Since the pouring of concrete began to cement the basic end of the heat, usually about 30 days. Two characteristics of this stage, one release of a large number of hydration heat of cement, the second is the elastic modulus on the coagulation of dramatic changes. As the elastic modulus of this period to form residual stress in the concrete.
(2) Medium-term: the role of heat from the cement concrete base until the end of cooling to a stable temperature only, this period, mainly due to thermal stress and external cooling of concrete caused by temperature changes, stress and early formation of these residual stress overlay of coagulation during this period little change in the elastic modulus.
(3) late: after the concrete has cooled during the operation. Thermal stress is mainly caused by external temperature changes, these stresses and residual stress in the first two-phase superposition.
According to the temperature stress-induced causes can be divided into two categories:
(1) self stress: There are no constraints on the boundary or completely static structure, if t
According to the formation of thermal stress can be divided into the following three stages:
(1) Early: Since the pouring of concrete began to cement the basic end of the heat, usually about 30 days. Two characteristics of this stage, one release of a large number of hydration heat of cement, the second is the elastic modulus on the coagulation of dramatic changes. As the elastic modulus of this period to form residual stress in the concrete.
(2) Medium-term: the role of heat from the cement concrete base until the end of cooling to a stable temperature only, this period, mainly due to thermal stress and external cooling of concrete caused by temperature changes, stress and early formation of these residual stress overlay of coagulation during this period little change in the elastic modulus.
(3) late: after the concrete has cooled during the operation. Thermal stress is mainly caused by external temperature changes, these stresses and residual stress in the first two-phase superposition.
According to the temperature stress-induced causes can be divided into two categories:
(1) self stress: There are no constraints on the boundary or completely static structure, if t
he internal temperature distribution is nonlinear, due to structural constraints arising from their co-temperature stress. For example, the bridge piers, structure size is relatively large, concrete cooling the surface temperature is low, the internal temperature is high, the surface tensile stress, compressive stress occurs in the middle.
(2) restraint stress: the structure of all or part of the border by the external constraints, not free to deformation caused by stress. Such as concrete roof and parapet concrete box girder.
Both the temperature and stress is often caused by shrinkage of concrete joint action of stress.
Accurate according to the known temperature in order to analyze the thermal stress distribution, size is a more complex task. In most cases, the need to rely on model test or numerical calculation. Creep of concrete so that there is a large thermal stress relaxation, thermal stress calculation, we must consider the impact of creep, will not dwell here on the specific calculation.
3, temperature control and prevention measures for cracks
(2) restraint stress: the structure of all or part of the border by the external constraints, not free to deformation caused by stress. Such as concrete roof and parapet concrete box girder.
Both the temperature and stress is often caused by shrinkage of concrete joint action of stress.
Accurate according to the known temperature in order to analyze the thermal stress distribution, size is a more complex task. In most cases, the need to rely on model test or numerical calculation. Creep of concrete so that there is a large thermal stress relaxation, thermal stress calculation, we must consider the impact of creep, will not dwell here on the specific calculation.
3, temperature control and prevention measures for cracks
To prevent cracking, reduce temperature stress can control the temperature and improve the constraints of two aspects.
Temperature control measures are as follows:
(1) The improvement of aggregate gradation, with a dry hard concrete, mixed with mixture, add air-entraining agent or a plasticizing agent measures to reduce the amount of cement in concrete;
(2) when the mixing of concrete will be crushed stone and water or water cooling to reduce the temperature of the concrete pouring;
(3) hot days when the pouring of concrete pouring to reduce the thickness of heat by pouring level;
(4) the laying of water pipes in the concrete, which leads to water cooling;
(5) provides a reasonable form removal time, the surface heat when temperatures plunged to avoid dramatic concrete surface temperature gradient;
(6) Construction of Concrete Blocks and long-term exposure to surface or thin-walled structure, insulation measures taken in the cold season;
Temperature control measures are as follows:
(1) The improvement of aggregate gradation, with a dry hard concrete, mixed with mixture, add air-entraining agent or a plasticizing agent measures to reduce the amount of cement in concrete;
(2) when the mixing of concrete will be crushed stone and water or water cooling to reduce the temperature of the concrete pouring;
(3) hot days when the pouring of concrete pouring to reduce the thickness of heat by pouring level;
(4) the laying of water pipes in the concrete, which leads to water cooling;
(5) provides a reasonable form removal time, the surface heat when temperatures plunged to avoid dramatic concrete surface temperature gradient;
(6) Construction of Concrete Blocks and long-term exposure to surface or thin-walled structure, insulation measures taken in the cold season;
Measures to improve the constraints:
(1) reasonable parting block;
(2) to avoid excessive fluctuations basis;
(3) reasonable arrangements for the construction process, to avoid the excessive height and long-term exposure to the side;
In addition, improving the performance of concrete and improve the crack resistance, enhance conservation, to prevent surface shrinkage, in particular, to ensure the quality of concrete is very important to prevent fractures, special attention should be avoided through the cracks, appears to restore the integrity of its structure is very difficult, so the construction should be to prevent the occurrence of cracks in the main cross-cutting.
In concrete construction, in order to improve the turnover rate of the template, often require new concrete form removal as soon as possible. When the temperature is higher than the temperature of concrete removal time should be due consideration, in order to avoid the early cracks in the concrete surface. New casting early form removal, on the surface caused by large tensile stress, a "thermal shock" phenomenon. Early in the concrete pourin
(1) reasonable parting block;
(2) to avoid excessive fluctuations basis;
(3) reasonable arrangements for the construction process, to avoid the excessive height and long-term exposure to the side;
In addition, improving the performance of concrete and improve the crack resistance, enhance conservation, to prevent surface shrinkage, in particular, to ensure the quality of concrete is very important to prevent fractures, special attention should be avoided through the cracks, appears to restore the integrity of its structure is very difficult, so the construction should be to prevent the occurrence of cracks in the main cross-cutting.
In concrete construction, in order to improve the turnover rate of the template, often require new concrete form removal as soon as possible. When the temperature is higher than the temperature of concrete removal time should be due consideration, in order to avoid the early cracks in the concrete surface. New casting early form removal, on the surface caused by large tensile stress, a "thermal shock" phenomenon. Early in the concrete pourin
g, the distribution of heat of hydration, the surface tension caused considerable stress, then the surface temperature is higher than the temperature at this time removal of the template, the surface temperature plunged, would inevitably lead to the temperature gradient, the surface attached to a tensile stress, thermal stress superposition and hydration, along with concrete shrinkage, the surface tensile stress to a great value, there is the risk of lead fracture, but after removal of the template in a timely manner if the surface coverage of a light insulation materials, such as foam sponge, concrete surface to prevent excessive tensile stress, a significant effect.
Reinforced concrete for large thermal stress has little effect, because the large volume of concrete with reinforcement ratio is very low. Only a reinforced concrete impact. Not too high in temperature and stress below the yield limit under the conditions of the properties of steel is stable, but with the stress state, independent of time and temperature. Linear expansion coefficient of steel and concrete in linear expansion coefficient difference is small, changes in temperature between the two occurs only within a very small stress. The elastic modulus of the steel elastic modulus of concrete 7 to 15 times, when the stress reac
Reinforced concrete for large thermal stress has little effect, because the large volume of concrete with reinforcement ratio is very low. Only a reinforced concrete impact. Not too high in temperature and stress below the yield limit under the conditions of the properties of steel is stable, but with the stress state, independent of time and temperature. Linear expansion coefficient of steel and concrete in linear expansion coefficient difference is small, changes in temperature between the two occurs only within a very small stress. The elastic modulus of the steel elastic modulus of concrete 7 to 15 times, when the stress reac
hes the tensile strength of concrete cracking, reinforcement of stress will not exceed 100 ~ 200kg/cm2 .. So you want to use in concrete reinforced to prevent the emergence of small cracks is difficult. However, the cracks within the structure was reinforced generally becomes more than the number, spacing is small, a smaller width and depth. And if the diameter of thin reinforced when close spacing, to improve the crack resistance of concrete is better. Concrete and reinforced concrete structures on the surface often thin and shallow cracks occur, most of which are shrinkage cracks. While this is generally shallow cracks, but it strength and durability of the structure is still a certain extent.
To ensure the quality of concrete to prevent cracking and improve durability of concrete, the proper use of additives is one of the measures to reduce cracking. Such as using less water, crack resistance, the author summarizes in practice its main role is to:
(1) there are a large number of pores of concrete road, water evaporating capillary tension generated in a capillary, so that concrete shrinkage deformation. Diameter of capillary pores increases the surface tension can be reduced, but will reduce the strength of concrete. The theory of surface tension early in the sixties had been recognized internati
To ensure the quality of concrete to prevent cracking and improve durability of concrete, the proper use of additives is one of the measures to reduce cracking. Such as using less water, crack resistance, the author summarizes in practice its main role is to:
(1) there are a large number of pores of concrete road, water evaporating capillary tension generated in a capillary, so that concrete shrinkage deformation. Diameter of capillary pores increases the surface tension can be reduced, but will reduce the strength of concrete. The theory of surface tension early in the sixties had been recognized internati
onally.
(2) water-cement ratio is an important factor affecting concrete shrinkage, the use of water-reducing agent can crack concrete water consumption reduced by 25%.
(3) the amount of cement is also an important factor in shrinkage of concrete, mixed addition and subtraction of water in the crack resistance of the concrete under the conditions of maintaining the strength of concrete can be reduced by 15% of the amount of cement, aggregate consumption by increasing its volume to add.
(4) water-reducing agent can improve the cracking slurry consistency and reduce the bleeding of concrete, reduce shrinkage deformation Shen.
(5) improve the slurry and the aggregate bond strength, improved crack resistance of concrete.
(6) concrete in the contraction of restrained tensile stress, tensile strength of concrete when the tensile stress is greater than when the cracks will be generated. Water-reducing agent can effectively improve the cracking of the concrete tensile strength, a substantial increase in the crack resistance of concrete.
(2) water-cement ratio is an important factor affecting concrete shrinkage, the use of water-reducing agent can crack concrete water consumption reduced by 25%.
(3) the amount of cement is also an important factor in shrinkage of concrete, mixed addition and subtraction of water in the crack resistance of the concrete under the conditions of maintaining the strength of concrete can be reduced by 15% of the amount of cement, aggregate consumption by increasing its volume to add.
(4) water-reducing agent can improve the cracking slurry consistency and reduce the bleeding of concrete, reduce shrinkage deformation Shen.
(5) improve the slurry and the aggregate bond strength, improved crack resistance of concrete.
(6) concrete in the contraction of restrained tensile stress, tensile strength of concrete when the tensile stress is greater than when the cracks will be generated. Water-reducing agent can effectively improve the cracking of the concrete tensile strength, a substantial increase in the crack resistance of concrete.
(7) compacting concrete admixture additive can, and can effectively improve the carbonation resistance of concrete to reduce the carbonation shrinkage.
(8) mixed with water-reducing retarding crack resistance of concrete time to properly, effectively prevent the cement on the basis of the rapid heat of hydration to avoid long-term non-condensable cement brought plastic shrinkage increases.
(9) mixed with a good admixture of concrete workability, easy to touch the flat surface to form a micro-film to reduce evaporation and reduce drying shrinkage.
Many have a retarding admixture to increase workability, improve the function of plasticity, we in engineering practice in this regard should be more experimental comparison and research, than simply by improving the external conditions, may be more simple and economical.
4 early curing of concrete
Practice shows that cracks in concrete common, most of the surface cracks of different depth, mainly because of the temperature gradient caused by the sudden drop in temperature in cold areas are also easy to form cracks. So, to say the insulation of concret
(8) mixed with water-reducing retarding crack resistance of concrete time to properly, effectively prevent the cement on the basis of the rapid heat of hydration to avoid long-term non-condensable cement brought plastic shrinkage increases.
(9) mixed with a good admixture of concrete workability, easy to touch the flat surface to form a micro-film to reduce evaporation and reduce drying shrinkage.
Many have a retarding admixture to increase workability, improve the function of plasticity, we in engineering practice in this regard should be more experimental comparison and research, than simply by improving the external conditions, may be more simple and economical.
4 early curing of concrete
Practice shows that cracks in concrete common, most of the surface cracks of different depth, mainly because of the temperature gradient caused by the sudden drop in temperature in cold areas are also easy to form cracks. So, to say the insulation of concret
e to prevent cracks in the surface is particularly important in early.
From the viewpoint of thermal stress, thermal insulation should meet the following requirements:
1) prevent the concrete and the concrete surface temperature difference between inside and outside the gradient, to prevent surface cracks.
2) prevent the concrete super-cool, should try to try to make concrete the construction period of not less than the minimum temperature on the stability of the temperature of concrete used.
3) to prevent cold and old concrete to reduce the constraints between the new and old concrete.
Early curing of concrete, the main purpose is to maintain proper temperature and humidity conditions in order to achieve the effect of two aspects, one of the concrete from adverse temperature and humidity deformation of the invasion, to prevent the harmful shrinkage and shrinkage. On the one hand to smooth the cement hydration in order to meet the design strength and crack resistance.
From the viewpoint of thermal stress, thermal insulation should meet the following requirements:
1) prevent the concrete and the concrete surface temperature difference between inside and outside the gradient, to prevent surface cracks.
2) prevent the concrete super-cool, should try to try to make concrete the construction period of not less than the minimum temperature on the stability of the temperature of concrete used.
3) to prevent cold and old concrete to reduce the constraints between the new and old concrete.
Early curing of concrete, the main purpose is to maintain proper temperature and humidity conditions in order to achieve the effect of two aspects, one of the concrete from adverse temperature and humidity deformation of the invasion, to prevent the harmful shrinkage and shrinkage. On the one hand to smooth the cement hydration in order to meet the design strength and crack resistance.
Appropriate conditions of temperature and humidity are interrelated. Insulation measures are often on the coagulation has moisturizing effect.
From the theoretical analysis, water contained in fresh concrete can meet the requirements of more than cement hydration. However, due to evaporation and other factors often cause water loss, and thus delay or hinder the hydration of cement, concrete surface and directly affected by the most vulnerable to such adverse effects. So the first few days after concrete pouring is the conservation of a critical period in the construction should be earnestly pay attention to it.
5 Conclusion
Over the construction of concrete cracks in the relationship between temperature and carried out the initial theory and practice of, despite all the academic cracks in the concrete and calculation methods are different theories, but for specific advice for prevention and improvement measures is relatively uniform the same time, the application effect in practice is relatively good, concrete construction depends on our seeing much comparison, more analysis after problems, and more sum up, dealing with a variety of preventive measures, concrete cracks are completely avoidable.
From the theoretical analysis, water contained in fresh concrete can meet the requirements of more than cement hydration. However, due to evaporation and other factors often cause water loss, and thus delay or hinder the hydration of cement, concrete surface and directly affected by the most vulnerable to such adverse effects. So the first few days after concrete pouring is the conservation of a critical period in the construction should be earnestly pay attention to it.
5 Conclusion
Over the construction of concrete cracks in the relationship between temperature and carried out the initial theory and practice of, despite all the academic cracks in the concrete and calculation methods are different theories, but for specific advice for prevention and improvement measures is relatively uniform the same time, the application effect in practice is relatively good, concrete construction depends on our seeing much comparison, more analysis after problems, and more sum up, dealing with a variety of preventive measures, concrete cracks are completely avoidable.
混凝土裂缝 1 裂缝的原因 混凝土中产生裂缝有多种原因，主要是温度和湿度的变化，混凝土的脆性和不均匀性，以及结构不合理，原材料不合格（如碱骨料反应），模板变形，基础不均匀沉降等。
混凝土硬化期间水泥放出大量水化热，内部温度不断上升，在表面引起拉应力。后期在降温过程中，由于受到基础或老混凝上的约束，又会在混凝土内部出现拉应力。气温的降低也会在混凝土表面引起很大的拉应力。当这些拉应力超出混凝土的抗裂能力时，即会出现裂缝。许多混凝土的内部湿度变化很小或变化较慢，但表面湿度可能变化较大或发生剧烈变化。如养护不周、时干时湿，表面干缩形变受到内部混凝土的约束，也往往导致裂缝。混凝土是一种脆性材料，抗拉强度是抗压强度的1／10左右，短期加荷时的极限拉伸变形只有（0.6～1.0）×104， 长期加荷时的极限位伸变形也只有（1.2～2.0）×104.由于原材料不均匀，水灰比不稳定，及运输和浇筑过程中的离析现象，在同一块混凝土中其抗拉强度又是不均匀的，存在着许多抗拉能力很低，易于出现裂缝的薄弱部位。在钢筋混凝土中，拉应力主要是由钢筋承担，混凝土只是承受压应力。在素混凝土内或钢筋混凝上的边缘部位如果结构内出现了拉应力，则须依靠混凝土自身承担。一般设计中均要求不出现拉应力或者只出现很
混凝土硬化期间水泥放出大量水化热，内部温度不断上升，在表面引起拉应力。后期在降温过程中，由于受到基础或老混凝上的约束，又会在混凝土内部出现拉应力。气温的降低也会在混凝土表面引起很大的拉应力。当这些拉应力超出混凝土的抗裂能力时，即会出现裂缝。许多混凝土的内部湿度变化很小或变化较慢，但表面湿度可能变化较大或发生剧烈变化。如养护不周、时干时湿，表面干缩形变受到内部混凝土的约束，也往往导致裂缝。混凝土是一种脆性材料，抗拉强度是抗压强度的1／10左右，短期加荷时的极限拉伸变形只有（0.6～1.0）×104， 长期加荷时的极限位伸变形也只有（1.2～2.0）×104.由于原材料不均匀，水灰比不稳定，及运输和浇筑过程中的离析现象，在同一块混凝土中其抗拉强度又是不均匀的，存在着许多抗拉能力很低，易于出现裂缝的薄弱部位。在钢筋混凝土中，拉应力主要是由钢筋承担，混凝土只是承受压应力。在素混凝土内或钢筋混凝上的边缘部位如果结构内出现了拉应力，则须依靠混凝土自身承担。一般设计中均要求不出现拉应力或者只出现很
小的拉应力。但是在施工中混凝土由最高温度冷却到运转时期的稳定温度，往往在混凝土内部引起相当大的拉应力。有时温度应力可超过其它外荷载所引起的应力，因此掌握温度应力的变化规律对于进行合理的结构设计和施工极为重要。 2 温度应力的分析
根据温度应力的形成过程可分为以下三个阶段：
（1）早期：自浇筑混凝土开始至水泥放热基本结束，一般约30天。这个阶段的两个特征，一是水泥放出大量的水化热，二是混凝上弹性模量的急剧变化。由于弹性模量的变化，这一时期在混凝土内形成残余应力。
（2）中期：自水泥放热作用基本结束时起至混凝土冷却到稳定温度时止，这个时期中，温度应力主要是由于混凝土的冷却及外界气温变化所引起，这些应力与早期形成的残余应力相叠加，在此期间混凝上的弹性模量变化不大。
（3）晚期：混凝土完全冷却以后的运转时期。温度应力主要是外界气温变化所引起，这些应力与前两种的残余应力相迭加。
根据温度应力引起的原因可分为两类：
（1）自生应力：边界上没有任何约束或完全静止的结构，如果内部温度是非线性分布的，由于结构本身互相约束而出现的温度应力。例如，桥梁墩身，结构尺寸相对较大，混凝土冷
（1）早期：自浇筑混凝土开始至水泥放热基本结束，一般约30天。这个阶段的两个特征，一是水泥放出大量的水化热，二是混凝上弹性模量的急剧变化。由于弹性模量的变化，这一时期在混凝土内形成残余应力。
（2）中期：自水泥放热作用基本结束时起至混凝土冷却到稳定温度时止，这个时期中，温度应力主要是由于混凝土的冷却及外界气温变化所引起，这些应力与早期形成的残余应力相叠加，在此期间混凝上的弹性模量变化不大。
（3）晚期：混凝土完全冷却以后的运转时期。温度应力主要是外界气温变化所引起，这些应力与前两种的残余应力相迭加。
根据温度应力引起的原因可分为两类：
（1）自生应力：边界上没有任何约束或完全静止的结构，如果内部温度是非线性分布的，由于结构本身互相约束而出现的温度应力。例如，桥梁墩身，结构尺寸相对较大，混凝土冷
却时表面温度低，内部温度高，在表面出现拉应力，在中间出现压应力。
（2）约束应力：结构的全部或部分边界受到外界的约束，不能自由变形而引起的应力。如箱梁顶板混凝土和护栏混凝土。
这两种温度应力往往和混凝土的干缩所引起的应力共同作用。
要想根据已知的温度准确分析出温度应力的分布、大小是一项比较复杂的工作。在大多数情况下，需要依靠模型试验或数值计算。混凝土的徐变使温度应力有相当大的松驰，计算温度应力时，必须考虑徐变的影响，具体计算这里就不再细述。
（2）约束应力：结构的全部或部分边界受到外界的约束，不能自由变形而引起的应力。如箱梁顶板混凝土和护栏混凝土。
这两种温度应力往往和混凝土的干缩所引起的应力共同作用。
要想根据已知的温度准确分析出温度应力的分布、大小是一项比较复杂的工作。在大多数情况下，需要依靠模型试验或数值计算。混凝土的徐变使温度应力有相当大的松驰，计算温度应力时，必须考虑徐变的影响，具体计算这里就不再细述。
3 温度的控制和防止裂缝的措施
为了防止裂缝，减轻温度应力可以从控制温度和改善约束条件两个方面着手。
控制温度的措施如下：
（1）采用改善骨料级配，用干硬性混凝土，掺混合料，加引气剂或塑化剂等措施以减少混凝土中的水泥用量；
（2）拌合混凝土时加水或用水将碎石冷却以降低混凝土的浇筑温度；
（3）热天浇筑混凝土时减少浇筑厚度，利用浇筑层面散热；
控制温度的措施如下：
（1）采用改善骨料级配，用干硬性混凝土，掺混合料，加引气剂或塑化剂等措施以减少混凝土中的水泥用量；
（2）拌合混凝土时加水或用水将碎石冷却以降低混凝土的浇筑温度；
（3）热天浇筑混凝土时减少浇筑厚度，利用浇筑层面散热；
（4）在混凝土中埋设水管，通入冷水降温；
（5）规定合理的拆模时间，气温骤降时进行表面保温，以免混凝土表面发生急剧的温度梯度；
（6）施工中长期暴露的混凝土浇筑块表面或薄壁结构，在寒冷季节采取保温措施；
改善约束条件的措施是：
（1）合理地分缝分块；
（2）避免基础过大起伏；
（3）合理的安排施工工序，避免过大的高差和侧面长期暴露；
此外，改善混凝土的性能，提高抗裂能力，加强养护，防止表面干缩，特别是保证混凝土的质量对防止裂缝是十分重要，应特别注意避免产生贯穿裂缝，出现后要恢复其结构的整体性是十分困难的，因此施工中应以预防贯穿性裂缝的发生为主。
在混凝土的施工中，为了提高模板的周转率，往往要求新浇筑的混凝土尽早拆模。当混凝土温度高于气温时应适当考虑拆模时间，以免引起混凝土表面的早期裂缝。新浇筑早期拆模，在表面引起很大的拉应力，出现“温度冲击”现象。在混凝土浇筑初期，由于水化热的散发，表面引起相当大的拉应力，此时表面温度亦较气温为高，此时拆除模板，表面温度骤降，必
（5）规定合理的拆模时间，气温骤降时进行表面保温，以免混凝土表面发生急剧的温度梯度；
（6）施工中长期暴露的混凝土浇筑块表面或薄壁结构，在寒冷季节采取保温措施；
改善约束条件的措施是：
（1）合理地分缝分块；
（2）避免基础过大起伏；
（3）合理的安排施工工序，避免过大的高差和侧面长期暴露；
此外，改善混凝土的性能，提高抗裂能力，加强养护，防止表面干缩，特别是保证混凝土的质量对防止裂缝是十分重要，应特别注意避免产生贯穿裂缝，出现后要恢复其结构的整体性是十分困难的，因此施工中应以预防贯穿性裂缝的发生为主。
在混凝土的施工中，为了提高模板的周转率，往往要求新浇筑的混凝土尽早拆模。当混凝土温度高于气温时应适当考虑拆模时间，以免引起混凝土表面的早期裂缝。新浇筑早期拆模，在表面引起很大的拉应力，出现“温度冲击”现象。在混凝土浇筑初期，由于水化热的散发，表面引起相当大的拉应力，此时表面温度亦较气温为高，此时拆除模板，表面温度骤降，必
然引起温度梯度，从而在表面附加一拉应力，与水化热应力迭加，再加上混凝土干缩，表面的拉应力达到很大的数值，就有导致裂缝的危险，但如果在拆除模板后及时在表面覆盖一轻型保温材料，如泡沫海棉等，对于防止混凝土表面产生过大的拉应力，具有显著的效果。
加筋对大体积混凝土的温度应力影响很小，因为大体积混凝土的含筋率极低。只是对一般钢筋混凝土有影响。在温度不太高及应力低于屈服极限的条件下，钢的各项性能是稳定的，而与应力状态、时间及温度无关。钢的线胀系数与混凝土线胀系数相差很小，在温度变化时两者间只发生很小的内应力。由于钢的弹性模量为混凝土弹性模量的7~15倍，当内混凝土应力达到抗拉强度而开裂时，钢筋的应力将不超过100~200kg／cm2..因此，在混凝土中想要利用钢筋来防止细小裂缝的出现很困难。但加筋后结构内的裂缝一般就变得数目多、间距小、宽度与深度较小了。而且如果钢筋的直径细而间距密时，对提高混凝土抗裂性的效果较好。混凝土和钢筋混凝土结构的表面常常会发生细而浅的裂缝，其中大多数属于干缩裂缝。虽然这种裂缝一般都较浅，但它对结构的强度和耐久性仍有一定的影响。
为保证混凝土工程质量，防止开裂，提高混凝土的耐久性，正确使用外加剂也是减少开裂的措施之一。例如使用减水防裂剂，笔者在实践中总结出其主要作用为：
（1）混凝土中存在大量毛细孔道，水蒸发后毛细管中产生毛细管张力，使混凝土干缩变形。
加筋对大体积混凝土的温度应力影响很小，因为大体积混凝土的含筋率极低。只是对一般钢筋混凝土有影响。在温度不太高及应力低于屈服极限的条件下，钢的各项性能是稳定的，而与应力状态、时间及温度无关。钢的线胀系数与混凝土线胀系数相差很小，在温度变化时两者间只发生很小的内应力。由于钢的弹性模量为混凝土弹性模量的7~15倍，当内混凝土应力达到抗拉强度而开裂时，钢筋的应力将不超过100~200kg／cm2..因此，在混凝土中想要利用钢筋来防止细小裂缝的出现很困难。但加筋后结构内的裂缝一般就变得数目多、间距小、宽度与深度较小了。而且如果钢筋的直径细而间距密时，对提高混凝土抗裂性的效果较好。混凝土和钢筋混凝土结构的表面常常会发生细而浅的裂缝，其中大多数属于干缩裂缝。虽然这种裂缝一般都较浅，但它对结构的强度和耐久性仍有一定的影响。
为保证混凝土工程质量，防止开裂，提高混凝土的耐久性，正确使用外加剂也是减少开裂的措施之一。例如使用减水防裂剂，笔者在实践中总结出其主要作用为：
（1）混凝土中存在大量毛细孔道，水蒸发后毛细管中产生毛细管张力，使混凝土干缩变形。
增大毛细孔径可降低毛细管表面张力，但会使混凝土强度降低。这个表面张力理论早在六十年代就已被国际上所确认。
（2）水灰比是影响混凝土收缩的重要因素，使用减水防裂剂可使混凝土用水量减少25％。
（3）水泥用量也是混凝土收缩率的重要因素，掺加减水防裂剂的混凝土在保持混凝土强度的条件下可减少15％的水泥用量，其体积用增加骨料用量来补充。
（4）减水防裂剂可以改善水泥浆的稠度，减少混凝土泌水，减少沉缩变形。
（5）提高水泥浆与骨料的粘结力，提高的混凝土抗裂性能。
（pouring6）混凝土在收缩时受到约束产生拉应力，当拉应力大于混凝土抗拉强度时裂缝就会产生。减水防裂剂可有效的提高的混凝土抗拉强度，大幅提高混凝土的抗裂性能。
（7）掺加外加剂可使混凝土密实性好，可有效地提高混凝土的抗碳化性，减少碳化收缩。
（8）掺减水防裂剂后混凝土缓凝时间适当，在有效防止水泥迅速水化放热基础上，避免因水泥长期不凝而带来的塑性收缩增加。
（9）掺外加剂混凝土和易性好，表面易摸平，形成微膜，减少水分蒸发，减少干燥收缩.
许多外加剂都有缓凝、增加和易性、改善塑性的功能，我们在工程实践中应多进行这方面的实验对比和研究，比单纯的靠改善外部条件，可能会更加简捷、经济。
（2）水灰比是影响混凝土收缩的重要因素，使用减水防裂剂可使混凝土用水量减少25％。
（3）水泥用量也是混凝土收缩率的重要因素，掺加减水防裂剂的混凝土在保持混凝土强度的条件下可减少15％的水泥用量，其体积用增加骨料用量来补充。
（4）减水防裂剂可以改善水泥浆的稠度，减少混凝土泌水，减少沉缩变形。
（5）提高水泥浆与骨料的粘结力，提高的混凝土抗裂性能。
（pouring6）混凝土在收缩时受到约束产生拉应力，当拉应力大于混凝土抗拉强度时裂缝就会产生。减水防裂剂可有效的提高的混凝土抗拉强度，大幅提高混凝土的抗裂性能。
（7）掺加外加剂可使混凝土密实性好，可有效地提高混凝土的抗碳化性，减少碳化收缩。
（8）掺减水防裂剂后混凝土缓凝时间适当，在有效防止水泥迅速水化放热基础上，避免因水泥长期不凝而带来的塑性收缩增加。
（9）掺外加剂混凝土和易性好，表面易摸平，形成微膜，减少水分蒸发，减少干燥收缩.
许多外加剂都有缓凝、增加和易性、改善塑性的功能，我们在工程实践中应多进行这方面的实验对比和研究，比单纯的靠改善外部条件，可能会更加简捷、经济。
4 混凝土的早期养护
实践证明，混凝土常见的裂缝，大多数是不同深度的表面裂缝，其主要原因是温度梯度造成寒冷地区的温度骤降也容易形成裂缝。因此说混凝土的保温对防止表面早期裂缝尤其重要。
从温度应力观点出发，保温应达到下述要求：
1）防止混凝土内外温度差及混凝土表面梯度，防止表面裂缝。
2）防止混凝土超冷，应该尽量设法使混凝土的施工期最低温度不低于混凝土使用期的稳定温度。
3）防止老混凝土过冷，以减少新老混凝土间的约束。
混凝土的早期养护，主要目的在于保持适宜的温湿条件，以达到两个方面的效果，一方面使混凝土免受不利温、湿度变形的侵袭，防止有害的冷缩和干缩。一方面使水泥水化作用顺利进行，以期达到设计的强度和抗裂能力。
适宜的温湿度条件是相互关联的。混凝上的保温措施常常也有保湿的效果。
从理论上分析，新浇混凝土中所含水分完全可以满足水泥水化的要求而有余。但由于蒸发等原因常引起水分损失，从而推迟或防碍水泥的水化，表面混凝土最容易而且直接受到这种不利影响。因此混凝土浇筑后的最初几天是养护的关键时期，在施工中应切实重视起来。
从温度应力观点出发，保温应达到下述要求：
1）防止混凝土内外温度差及混凝土表面梯度，防止表面裂缝。
2）防止混凝土超冷，应该尽量设法使混凝土的施工期最低温度不低于混凝土使用期的稳定温度。
3）防止老混凝土过冷，以减少新老混凝土间的约束。
混凝土的早期养护，主要目的在于保持适宜的温湿条件，以达到两个方面的效果，一方面使混凝土免受不利温、湿度变形的侵袭，防止有害的冷缩和干缩。一方面使水泥水化作用顺利进行，以期达到设计的强度和抗裂能力。
适宜的温湿度条件是相互关联的。混凝上的保温措施常常也有保湿的效果。
从理论上分析，新浇混凝土中所含水分完全可以满足水泥水化的要求而有余。但由于蒸发等原因常引起水分损失，从而推迟或防碍水泥的水化，表面混凝土最容易而且直接受到这种不利影响。因此混凝土浇筑后的最初几天是养护的关键时期，在施工中应切实重视起来。
5 结束语
以上对混凝土的施工温度与裂缝之间的关系进行了理论和实践上的初步探讨，虽然学术界对于混凝土裂缝的成因和计算方法有不同的理论，但对于具体的预防和改善措施意见还是比较统一，同时在实践中的应用效果也是比较好的，具体施工中要靠我们多观察、多比较，出现问题后多分析、多总结，结合多种预防处理措施，混凝土的裂缝是完全可以避免的。
以上对混凝土的施工温度与裂缝之间的关系进行了理论和实践上的初步探讨，虽然学术界对于混凝土裂缝的成因和计算方法有不同的理论，但对于具体的预防和改善措施意见还是比较统一，同时在实践中的应用效果也是比较好的，具体施工中要靠我们多观察、多比较，出现问题后多分析、多总结，结合多种预防处理措施，混凝土的裂缝是完全可以避免的。
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