返碱问题常出现于：干粉涂料、水泥基自流平、耐磨环氧地坪、填缝剂等干粉砂浆。 返碱的机理：碱性离子通过水份带出表面与钠、钙等离子在表面结晶和生成盐分并结晶形成白色粉末。 引起返碱的因素： ①硅酸盐水泥水化过程中，C3S和C2S水化生成C-S-H凝胶的同时，形成了大量的Ca(OH)2，Ca(OH)2除有一部分用以维持液相的碱度外，其它大多以晶体形态存在于水泥石中。Ca(OH)2是一种极易溶解的物质，在水泥基材料凝结硬化早期，其中的自由水会逐渐沿着内部毛细孔向外迁移，以补偿表面被蒸发掉的水分，在这一过程中，必然会将溶于其中的Ca(OH)2带出，当到达材料表面后，Ca(OH)2还会与空气中的CO2和水分发生化学反应生成不溶于水的白色沉淀CaCO3，附着在材料表面，这就是常见的表面泛白现象。这是最基本的一个因素，其他很多因素的本质和该条基本相同．
Alkali return often occurs in dry powder coatings, cement-based self-leveling, wear-resistant epoxy floors, sealants and other dry powder mortars. The mechanism of alkaline return: alkaline ions take out of the surface through water, and sodium, calcium plasma crystallize on the surface and form salt and crystallize to form white powder. The factors leading to the return of alkali: (1) during the hydration of Portland cement, C3S and C2S hydrated to form C-S-H gel, and at the same time, a large amount of Ca (OH) 2 was formed, while Ca (OH) 2 was used to maintain the alkalinity of the liquid phase, most of which existed in cement paste in the form of crystal. Ca (OH) 2 is a very soluble substance. In the early stage of setting and hardening of cement-based materials, free water will gradually migrate outward along the inner pores to compensate for the evaporated water on the surface. In this process, the dissolved Ca (OH) 2 will inevitably be removed. When it reaches the surface of the materials, Ca (OH) 2 will also be in the air. The chemical reaction of CO2 and water distribution produces white precipitate CaCO3 which is insoluble in water and adheres to the surface of the material. This is a common phenomenon of surface whitening. This is the most basic factor. The essence of many other factors is basically the same as that one.
②赶工期(常见于冬春季)，使用Na2SO4、CaCl2或以它们为主的复合产品作为早强剂，增加了水泥基材料的可溶性物质。 ③材料自身内部存在一定量的碱是先决条件，产生的原因水泥基材料属于多孔材料, 内部存在有大量尺寸不同的毛细孔, 成为可溶性物质在水的带动下从内部迁移出表面的通道。 ④水泥基材料即使硬化后比较干燥，但在使用过程中受到雨水浸泡，当水分渗入其内部，将其内部可溶性物质带出来，在表面反应并沉淀。
(2) During the rush period (usually in winter and spring), the use of Na2SO4, CaCl2 or their composite products as early strength agents increased the solubility of cement-based materials. (3) The existence of a certain amount of alkali in the material itself is a prerequisite. The reason is that the cement-based material belongs to porous material. There are a large number of different sizes of pores in the cement-based material, which can be used as a channel for soluble substances to migrate from the interior to the surface under the drive of water. (4) Even though the cement-based materials are relatively dry after hardening, they are soaked in rainwater during use. When the water infiltrates into the cement-based materials, the soluble substances in the cement-based materials are taken out and reacted on the surface and precipitated.
⑤湿度较大时，空气中的CO2与水分结合形成H2CO3，渗透到基材内部与Ca(OH)2化合成Ca(HCO3)2 , Ca(HCO3)2随着表面水分蒸发被带出来，直接结晶或者再与H2CO3反应生成CaCO3。 ⑥酸雨渗入基材内部，与基材中的碱性物质相结合并随着水分迁移到表面结晶，也会引起泛白。 返碱析出结晶在一定程度上可以增加基材表面的密实性，但是由于雨水循环作用，会将沉积在表面的可溶性的结晶物冲走，而基材内部由于可溶性物质的溶出，增大了孔隙率，降低了基材的抗渗性，从而会使盐、碱的析出作用加剧。
_When humidity is high, CO2 in the air combines with water to form H2CO3, which penetrates into the substrate and reacts with Ca (OH) 2 to synthesize Ca (HCO3) 2. Ca (HCO3) 2 is taken out with the evaporation of surface water and crystallizes directly or reacts with H2CO3 to form CaCO3. _Acid rain infiltrates into the substrate, combines with the alkaline substances in the substrate and crystallizes on the surface with moisture migration, which also causes whitening. Re-alkali precipitation crystallization can increase the surface compactness of the substrate to a certain extent, but the soluble crystals deposited on the surface will be washed away by rainwater cycling, and the porosity of the substrate will be increased and the impermeability of the substrate will be reduced due to the dissolution of soluble substances in the substrate. Intensifying.
减轻环氧地坪漆返碱的措施： ①没有根治的办法，只能尽可能降低其发生的几率，控制干粉砂浆搅拌过程的加水量。施工时环氧地坪材料不能泌水、完全干燥前表面不能与水接触；填缝剂施工过程务必在海绵擦拭后使表面水分尽快挥发，或使用不要太湿润的海绵。 ②尽量使用低碱水泥和外加剂。 ③优化配合比，增加水泥基材料密实度，减小毛细孔。例如使用其它熟料、填料替代部分水泥。 ④使用返碱抑制剂。如ELOTEX ERA-100，但经过使用不能完全改变这个情况，只能在某种程度上减轻返碱的情况，约100元/kg，掺量每吨约2.5kg，若掺量太高成本过高。 ⑤避免在干燥、刮风、低温环境条件下施工。 ⑥硅酸盐水泥与高强硫铝酸盐水泥复合使用有一定效果。原理如下：
Measures to alleviate the alkali return of epoxy floor paint: 1. There is no radical cure, only to reduce the probability of occurrence as far as possible, and control the amount of water added in the mixing process of dry powder mortar. During the construction, the floor material can not bleed, and the surface can not contact with water before completely drying; during the construction of sealant, it is necessary to make the surface moisture evaporate as soon as possible after sponge wiping, or to use a sponge that is not too wet. 2. Use low alkali cement and additives as much as possible. Third, optimize the mix proportion, increase the density of cement based materials and reduce Mao Xikong. For example, use other clinker and filler to replace part of cement. (4) use of alkali repressor. For example, ELOTEX ERA-100, but after use can not completely change this situation, can only reduce the return of alkali to a certain extent, about 100 yuan / kg, the amount of about 2.5 kg per ton, if the dosage is too high cost. Avoid construction under dry, windy and low temperature conditions. The combination of Portland cement and high strength sulphoaluminate cement has certain effect. The principles are as follows:
Ⅰ、硫铝酸盐水泥的2CaO?SiO2水化后生成的Ca(0H)2会与其它水化产物发生二次反应，形成新的化合物。3Ca(OH) 2+Al2O3?3H2O+3(CaSO4?2 H2O)+20 H2O→3 CaO?Al2O3?3CaSO4?32H2O。因此硫铝酸盐水泥水化产物不存在Ca(OH)2析晶。
I. Ca(0H)2 produced by hydration of 2CaO?SiO2 in sulphoaluminate cement reacts with other hydration products to form new compounds. 3Ca (OH) 2+Al2O3? 3H2O+3 (CaSO4? 2 H2O) +20 H2O to 3 CaO? Al2O3? 3CaSO4? Therefore, there is no Ca (OH) 2 crystallization in the hydration products of sulphoaluminate cement.
Ⅱ、硫铝酸盐水泥与普通硅酸盐水泥复合使用，水化过程中硫铝酸盐水泥会把普通硅酸盐水泥产生的多余的Ca(OH)2消耗掉，从根本上解决了返碱的问题。 重庆环氧地坪漆出现返碱后的处理方法： ①填缝剂出现严重返碱时，用低浓度的盐酸、草酸如５％的稀盐酸清洗，必要时用防水剂涂刷。 ②硫酸钠起霜应采用物理法处理。
II. When sulphoaluminate cement is combined with ordinary Portland cement, the excess Ca (OH) 2 produced by ordinary Portland cement will be consumed in the hydration process, and the problem of returning to alkali will be solved fundamentally. The treatment methods of Chongqing floor paint after alkali return are as follows: 1. When serious alkali return occurs in the sealant, clean it with low concentration of hydrochloric acid and oxalic acid such as 5% dilute hydrochloric acid, and brush it with waterproof agent if necessary. 2. Sodium sulfate frosting should be treated by physical method.
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