Effects of Curing of Winter Concreting on the Freeze-Thaw Resistance of Concrete

本研究的主要发现如下：(1)在混凝土浇筑后立即允许混凝土适度蒸发1-2天，然后提供足够的湿养护，是在不损害其强度发展的情况下显著提高混凝土冻融耐久性的有效和实用的方法。(2)养护结束时所需的混凝土抗压强度可能会随着水灰比的降低而降低。(3)即使在通常的水灰比范围内，比如45%到65%，降低水灰比可以大大缩短混凝土在寒冷天气下养护所需的时间。(4)由缓慢的冻融循环(如在自然天气条件下)引起的内部劣化被认为是孤立的和微小的，如果混凝土中残留足够的未水化水泥，则很容易通过水泥的水化产物来补救。(5)降低水灰比通过增加修补内部冻害的能力、增强对养护后由于强度增加而引起的劣化行为的抵抗能力来提高混凝土的冻融耐久性的益处。(6)全饱和混凝土的抗冻融性能完全取决于其抗压强度，只有当抗压强度超过230kgf/cm2时，才能获得满意的冻融耐久性。

The followings are main findings in this research.(1) The procedure of allowing moderate water-evaporation from concrete for 1 or 2 days immediately after placing of concrete, and, then, providing sufficient moist curing is an effective and practical way of remakably increasing the freeze-thaw durability of concrete without impairing its strength development.(2) The required compressive strength of concrete at the end of curing may be decreased as the water-cement ratio is decreased.(3) Even within the range of usual water-cement ratio, say, 45 to 65 %, the required periods of curing in cold weather concreting can be greatly shortened by lowering the ratio.(4) The inner deteriorations caused by an action of slow freezethaw cycles such as that under the natural weather conditions are considered to be isolated and minute ones, which can be remedied easily by the hydaration products of cement if a sufficient amount of unhydrated cement remains in the concrete.(5) Lowering water-cement ratio enhances the benefit of improving the freeze-thaw durability of concrete through such effects as the increased capability of remedying inner frost damge, increased resistance against deteriorating actions due to atrength increse after curing, decreased degree of water-saturation due to the continued cement hydration after curing.(6) The freeze-thaw resistance of fully saturated concrete with water is dependent entirely on its compressive strength, and satisfactory freeze-thaw durability can be obtainted only when its compressive exceeds about 230 kgf/cm^2.