摘要
"通过缓凝作用达到促凝效果"的含义是通过抑制石膏的溶解并用除石膏以外的外加剂抑制铝酸三钙(C3A)的水化这2个过程,配制一种加速水泥凝结的外加剂组分。小掺量(水泥含量的0.02%～0.03%)的邻苯二酚导致水泥的闪凝,这很可能是由于抑制了硫酸钙的分解以及C3A的快速水化。而这些小剂量的邻苯二酚好像对硅酸三钙(C3S)的水化没有影响。通过水化热和物理性能测试表明:由邻苯二酚导致的"闪凝",而其他比石膏掺量小的缓凝剂(例如:葡萄糖酸钠)可以减缓"闪凝",使样品较快凝结(即加速凝结)。但这些缓凝剂会延迟C3S的水化,从而也延迟水泥浆体强度的发展。如果假定上述机理是正确的,那么被抑制溶解的石膏会在水化后期发生反应,导致延迟钙矾石生成并使水泥浆体产生膨胀开裂。制备了掺加或不掺加这种外加剂的混凝土,测定了这些混凝土的线性膨胀和体积膨胀,以检验其发生膨胀的可能性,但是两个月后没有发现混凝土表现出非正常膨胀。
The ＂acceleration by retardation＂ concept is to make an admixture composition that will accelerate the setting of Portland cement by retarding two other processes;dissolution of gypsum and retardation of tricalcium aluminate（C3A） hydration by another admixture than gypsum.Small dosages of pyrocatechol（0.02%-0.03% of cement mass） leads to flash set of cement,most likely by inhibiting dissolution of calcium sulphate and thereby rapid hydration of C3A.These small dosages of pyrocatechol seem not to affect tricalcium silicate（C3S） hydration.It has been indicated by isothermal calorimetry and physically observed on excess paste that the ＂flash set＂ induced by pyrocatechol can be counteracted by other retarders in smaller dosages than gypsum（e.g.sodium gluconate）,leading to a faster setting（i.e.set acceleration） than the reference.However,these retarders delays onset of C3S hydration and may therefore also delay strength evolution.If the assumed mechanism of pyrocatechol is correct,the inhibited gypsum may react on a later stage and lead to a kind of delayed ettringite formation that could generate expansion and cracking.This possibility was checked out by casting concrete with and without similar admixture blends,and monitoring their linear and volumetric expansions.However,no abnormal expansion has been observed until present（2 months）.
出处
《硅酸盐学报》
EI
CAS
CSCD
北大核心
2010年第9期1618-1622,共5页
Journal of The Chinese Ceramic Society
关键词
促凝
膨胀
闪凝
石膏
水化热
缓凝
acceleration
expansion
flash set
gypsum
hydration heat
retardation
