MOISTURE CURINGEFFECT FOR CONCRETE IN STRUCTURE BY SHEATHING INPLACE ON HOTWEATHER

Abstract

For concrete in structures, moisture curing is important and has the large effect to the hydration of cement and the concrete properties after hardening. In the almost situations, moisture curing method of the vertical surface of wall and ceiling surface of under the slab are limited to cover with the sheathings. In the JASS 5 of AIJ, moisture curing period is specified prescribed days or compressive strength. Among these specifications, management due to compressive strength for moisture curing period is logical on the quality assurance of concrete and the working execution process. In the hot weather concreting, nevertheless, terminate of moisture curing at early age has apprehensiveness which is durability may be impaired. Then, in this research studied on the effects of moisture curing for concrete in structures from regarding to make wall model members, and considered management technique for moisture curing period from effects of the cement types and the water-cement ration.

Experiments were used 1,900 by 900 by 200 mm wall model members which made in summer and standard seasons. Moisture curing of members was used 12mm thick plywood for concrete formwork. Moisture curing terms were 1(2), 3, 5 and 7 days and removed plywood at these days. These wall model members were measured surface quality, compressive development and durability. Concrete using experiment wasmade in ready-mixed concrete plant, and these water-cement ratios were 0.45, 0.50 and 0.56.

As the results, effects of moisture curing periods were small on the concrete surface qualities of wall model members. That was, rebound number were same levels and coefficient of air permeability were Normal grade in spite of moisture curing periods. When removed plywood at 1 or 2 days, core compressive strength of those age were the above 10 N/mms that is management value of JASS 5. Furthermore, compressive strength differences of age 28 and 91 days were small due to different of moisture curing periods. Carbonation depth was large when terminated early moisture curing, but at over 3 days moisture curing periods, these values were same levels. However, effects of water-cement ratio for carbonation resistance were cleared than the moisture curing period.

On the evaluation for the effect of moisture curing for concrete in structures, strength development of concrete was confirmed enough too when moisture curing terminated early age. Moreover, carbonation depth of only water-cement ratio 0.56 of using ordinary portland cement was larger than the recommendation value of AIJ. As mentioned above, Water-cement ratio has an influence than the moisture curing period for carbonation resistance. Therefore, this report considered moisture curing period from the relationship between carbonation resistance and water-cement ratio. This relation was linearly, and the indoor water-cement ratios that satisfies the standard values of carbonation depth each planned service life class were 0.66 or less by short term, 0.55 or less by standard. These water-cement ratios were satisfied water-cement range that corresponding with durability design strength. From the above, if concrete proportion is designed to consider the durability design strength, durability for carbonation is considered to have enough resistance in spite of moisture curing period. In the hot weather concreting, from the above studying, when management for moisture curing period due to concrete compressive strength (10 N/mm²), concrete in structure is assessed that ensure the strength development and durability after terminate moisture curing.