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4 对混凝土性能影响
4．1对新拌混凝土性能影响
(1)和易性指混凝土拌合物易于施工操作，并能获得质量均匀，成型密实的混凝土性能，是一项综合技术性能。泵送剂主要组分是减水剂，能显著改善混凝土和易性。塌落度在120～250mm之间是适宜泵送的。塌落度过大，在泵送压力下弯头处容易产生离析而堵泵。塌落度过小吸入困难，无润滑层，摩擦阻力大，容易堵泵，泵送效率低。泵送剂在适宜掺量下能够提高混凝土塌落度80mm以上。在实际生产中，要制定适宜掺量。在使用前一定要做与水泥的适应性试验，保证正常泵送。
(2)粘聚性
指新拌混凝土组成材料之间有一定的粘聚力，使得混凝土不致发生分层和离析的性能。混凝土的粘聚性用观察的方法评定。粘聚性差的在试验时容易倒塌和离散；粘聚性好的砂浆对石子的包裹性能也好，不会在泵送时出现泵把砂浆泵出去，而在泵车的进料斗中留下大部分的石子，从而产生堵泵。加入好的泵送剂可使混凝土的粘聚性提高。砂率也是影响粘聚性的主要因素之一，砂率小容易离散。
(3)保水性
指新拌混凝土在施工过程中，保持水分不易析出的能力。保水性好坏也可在做塌落度试验时用观察的方法评定，塌落度筒提起后，有较多的水泥浆从底部流出时，说明保水性差。泌水率关系到泵送混凝土的均质性和可泵性，如果发生泌水，既影响混凝土质量，又会堵塞管道，造成堵泵。
(4)凝结时间
泵送剂有一定的缓凝作用，尤其是对初凝时间有一定的延缓。这是由于泵送混凝土对塌落度的保留值有一定的要求，在运送混凝土过程中，不能使塌落度损失过大，到工地后能够顺利泵送。泵送剂加入还可延缓混凝土早期水化热，降低在强度很低时的温度裂缝。
4．2 对硬化混凝土性能影响
(1)强度
常用的泵送剂减水率是较高的，混凝土强度有一定的提高。由于泵送混凝土中掺有粉煤灰、矿渣或两者都有，后期强度都有一定的提高，泵送混凝土流动性好，可在施工中充分密实，强度都有一定增加。
(2)收缩
收缩值取决于混凝土的水灰比和水泥用量，常用泵送剂减水率在15％以上，是比较高的，因此水泥干燥收缩值较小，混凝土收缩，是水泥水化引起的体积减小。低强度混凝土水泥用量少，但水灰比较大，收缩值也较大； 高强混凝土水灰比较小，但水泥用量较大，收缩值也较大。泵送剂中掺入减缩剂可降低混凝土收缩。
(3)耐久性
耐久性有冻融、硫酸盐侵蚀、碱骨料反应和CL-渗透。在大塌落度情况下，有比一般混凝土小的水灰比，可提高混凝土的密实度，使外界有害物质不能进入混凝土内部，从而提高混凝土耐久性，混凝土抗渗和冻融有一定提高。泵送混凝土都会掺入矿物料，由于矿物料细度较大，有助于填补混凝土微小空隙，提高混凝土密实度，对耐久性是有利的。碱骨料反应，骨料中的活性成分与水泥水化产物的碱反应，破坏混凝土结构。掺入泵送剂后，可大量使用矿物拌合料，能抑制碱骨料反应。
(4)碳化
碳化与混凝土水灰比、矿物掺合料、养护有关。碳化是混凝土表面与空气中CO2，反应，水泥中Ca(OH)2，与CO2，反应生成CaCO3 。粉煤灰掺量有最佳值，要根据不同水泥和粉煤灰来确定。泵送剂可降低混凝土水灰比，改善孔结构，使孔结构趋于完全封闭状态，空气中C02 和水不能进入混凝土内部，从而降低碳化。

Answer 1

4 on the performance of concrete
4.1 Properties of fresh concrete
(1) the workability of concrete mixture that is easy construction operations, and to obtain uniform quality, forming dense concrete properties, is a comprehensive technical performance. Pumping agent mainly composed of water-reducing agent, can significantly improve the workability of concrete. Slump in the 120 ~ 250mm suitable for pumping between the. Collapse through large, the pumping pressure elbow prone to segregation and blocking the pump. Inhaled through a small cave in the difficulties, no lubrication layer, frictional resistance and may easily block the pump, pumping efficiency is low. Pumping agent under the appropriate dosage can increase more than 80mm of concrete slump. In actual production, to develop appropriate content. Must be done prior to the use of adaptive testing with cement to ensure the normal pumping.
(2) cohesiveness
Composed of materials that fresh concrete had a certain cohesion, so concrete will not occur stratification and segregation performance. Concrete cohesiveness assessed using observation methods. Poor cohesiveness easy to fall in the test and discrete; cohesion and good performance of mortar on the stones of the package Ye Hao, when the pump will not pump out the mortar pump, pump truck into the hopper in the left big Some of the stones, resulting in blocking the pump. Adding a good pumping agent can improve the cohesiveness of concrete. Sand ratio is also affected cohesiveness one of the main factors, the rate of small sand easily separated.
(3) water retention
Refers to fresh concrete in the construction process, the ability to maintain moisture easily precipitated. Water retention may also be doing good or bad slump test methods used to observe the evaluation, after the slump cylinder filed, there is more water slurry from the bottom, indicating the poor water retention. Bleeding rate related to the homogeneity of pumping concrete pumping and can, if bleeding occurs, it will affect the quality of concrete, will plug the pipe, resulting in blocking the pump.
(4) setting time
Pumping agent has some retarding effect, especially on a certain set time delay. This is because the pumping of concrete slump retention value pairs have certain requirements for transporting concrete in the process, not to slump too much damage to the site in the smooth pumping. Concrete pumping agent to join the early heat of hydration can also delay and reduce the temperature in the low intensity of cracks.
4.2 Properties of hardened concrete
(1) strength
Commonly used to reduce water pumping rate is high, concrete strength has improved to some extent. As the pumping of concrete mixed with fly ash, slag, or both, have a certain increase in the late strength, pumping concrete flow, and can be fully compacted during construction, the intensity has certainly increased.
(2) contraction
Shrinkage depends on the concrete water-cement ratio and cement content, commonly used to reduce water pumping rate of 15% or more, is relatively high, so small value of drying shrinkage of cement, concrete shrinkage, is caused hydration of cement volume decreased . Low-strength concrete with less cement, but higher water-cement ratio, shrinkage is also large; high-strength concrete water-cement ratio is small but a larger amount of cement, the shrinkage is higher. Pumping agent mixed with reducing agent to reduce shrinkage.
(3) Durability
Durability with freezing and thawing, sulfate attack, alkali aggregate reaction and the CL-penetration. Slump in large cases, smaller than the water-cement ratio of concrete can increase the density of concrete, harmful substances can not enter the outside world inside the concrete to improve concrete durability, concrete permeability, and freeze it can improve. Pumping concrete are mixed with mineral material, due to greater fineness of mineral materials, concrete help to fill the small gaps and improve the density of concrete, the durability is favorable. Alkali aggregate reaction, the active ingredient in the aggregate and cement hydration products of the alkali reaction, destruction of concrete structures. Mixed pumping agent, the mixing can be substantial use of fossil material, can inhibit the alkali aggregate reaction.
(4) carbon
Carbonation of concrete water-cement ratio, admixtures, curing the. Carbonation of concrete surface and the air CO2, reaction, cement Ca (OH) 2, and CO2, the reaction of CaCO3. The best value of fly ash to cement and fly ash according to determine. Concrete pumping agent can reduce the water-cement ratio, improved pore structure, pore structure tends to make completely closed state, C02 in air and water can not enter inside the concrete, thus reducing the carbonation.