This research is to study the effect of mortar mixed with shrinkage reducing agent (polyoxyalkylene alkyl ether type), expansive additive (CaO type), and fly ash (hereinafter "SRA," "EX," and "FA," resp.). Moreover, steam curing was studied to improve the properties of mortar. The plastic shrinkage test was conducted by using the strain gauge embedded at 0.5 cm from the surface according to the ASTM C1579-06 standard within early age followed by the total shrinkage test and compressive strength test. The test results showed that mixing both the EX and SRA increases the plastic enlargement of the mortar during the early age more than using either the EX or SRA solely. The steam curing helps to reduce the plastic shrinkage when the mortar is added with the FA and SRA while adding the EX increases the enlargement compared to the normal curing. When the EX, SRA, and FA are all added to the mortar mixing, great attention should be paid due to the increase of greater enlargement. For the compressive strength view, the steam curing increases the compressive strength in all types of mixture. The steam curing significantly helps increasing the compressive strength of mortar with combination of EX, SRA, and FA. Nevertheless, the XRD and SEM tests explain such enlargement accordingly.

In the construction, it is inevitable to perform plaster work in hot weather which causes the dehydration and rapid shrinkage on the paste during the early age. This research shows the studies of reducing the plastic shrinkage of mortar during the early age with such additives as the Shrinkage Reducing Agent (SRA), the Expansive Additive (EX), and the Fly Ash (FA) in controlled temperatures at 30°C and 40°C, with relative humidity between 60% and 70% according to the ASTM C1579-06 standard, with the strain gauge installed at 0.5 cm.from the surface. The shrinkage rate was measured starting from the Initial Setting Time and every 10 minutes afterwards for 24 hours. The results show that high temperature effects the cracking and how to use different formulas of additive under different circumstances is considerably important. To use only one additive is not sufficient in high temperature. To use the SRA in addition to the EX enhances better expansion than to use only the EX. Moreover, it is recommended to pay close attention in adding large amount of the FA into mortar with the EX and SRA added which extremely enhances the expansion and potential cracking.

This research is part of the mortar’s plastic shrinkage study. Contents in this article is related to how the Expansive Additive (EX), Shrinkage Reducing Agent (SRA), and Fly Ash (FA) help to reduce and control the shrinkage and to compare the effectiveness of these substances used in the normal curing, i.e., at 30 °C and in the steam curing process by using the factorial design with 3 factors and to be divided into 2 levels. Factors to be studied are the amount of EX, SRA and FA replacement. The test of plastic shrinkage was conducted in accordance with the ASTM C1579-06 standard, placing the strain gauge 0.5 centimeters beneath the surface in the middle of the mold, recording the shrinkage rate starting from the initial setting time for 24 hours. The results showed that, in normal curing, the EX influences the expansion while, in steam curing, the EX and SRA significantly influences the expansion. To add the FA in high volume along with the EX significantly effects the expansion for both the normal and steam curing. Furthermore, the study model and equation for plastic shrinkage of mortar are presented in the form of factor proportion to be considered from the factorial design study basis.