Abstract—To obtain the high quality and essential workability of mortar, different types of superplasticizers are used. The superplasticizers are the chemical admixture used in the mix to improve the fluidity of mortar. Many factors influenced the superplasticizer to disperse the cement particle in the mortar. Nature and amount of replaced cement by slag, mixing procedure, delayed addition time, and heat stimulation technique of superplasticizer cause the varied effect on the fluidity of the cementitious material. In this experiment, the superplasticizers were heated for 1 hour under 60 °C in a thermostatic chamber. Furthermore, the effect of delayed addition time of heat stimulated superplasticizers (SP) was also analyzed. This method was applied to two types of polycarboxylic acid based ether SP (precast type superplasticizer (SP2) and ready- mix type superplasticizer (SP1)) in combination with a partial replacement of normal Portland cement with blast furnace slag (BFS) with 30% w/c ratio. On the other hands, the fluidity, air content, fresh density, and compressive strength for 7 and 28 days were studied. The results indicate that the addition time and heat stimulation technique improved the flow and air content, decreased the density, and slightly decreased the compressive strength of mortar. Moreover, the slag improved the flow of mortar by increasing the amount of slag, and the effect of external temperature of SP on the flow of mortar was decreased. In comparison, the flow of mortar was improved on 5-minute delay for both kinds of SP, but SP1 has improved the flow in all conditions. Most importantly, the transition points in both types of SP appear to be the same, at about 5±1 min. In addition, the optimum addition time of SP to mortar should be in this period. Keywords—Combined effect, delayed addition, heat stimulation, flow of mortar. I. INTRODUCTION SAGE of SP increases the workability of mortar and concrete. The SP is mainly using for these two purposes: 1. To control the flow characteristic, which is the most important parameter for the design of self-compacting concrete. 2. To reduce the w/c ratio, in order to obtain durable and high strength concrete. [1], [2], [6]. Faraidoon Rahmanzai is Graduate student of Civil Engineering, Tokai University, 4-1-1 Kitakaname, Hiratsuka, Kanagawa. Japan, 259-1292 (phone: 0463-58-1211(exp 6076), e-mail: frahmanzai@gmail.com). Mizuki Takigawa, Yu Bomura is with the Civil Engineering Tokai University 4-1-1 Kitakaname, Hiratsuka, kanagawa, Japan, 259-1292 (phone: 0463-58-1211(exp 6076), e-mail: 25concrete.4miz9@gmail.com, yu.bomura.tokai@gmail.com). Shigeyuki Date is professor in department of civil engineering, Tokai university, 4-1-1 Kitakaname, Hiratsuka, kanagawa, Japan, 259-1292 (phone: 0463-58-1211(exp 6076), e-mail: sdat@tokai-u.jp). Therefore, they are known as high range water reducer (SP). Heat stimulation technique also improves the fluidity of mortar and slightly decreased the compressive strength [3]-[5]. In this research, different amounts of normal Portland cement (OPC) (30%, 45%, and 60%) were replaced via BFS in combination with two kinds of polycarboxylic acid based SP (precast type (SP2) and ready-mix type (SP1)). By increasing the amount of BFS, the fluidity of mortar increased, and the amount of SP decreased. Moreover, the efficiency of external heating was decreased on the fluidity of mortar. Furthermore, by increasing the amount of BFS the compressive strength of mortar was decreased [7], [8]. On the other hand, the delayed addition time of SP increased the fluidity of mortar. By increasing the amount of BFS, the efficiency of delayed addition time on fluidity also decreased especially for more than 5 minutes [9]-[11]. Therefore, after 5-minute delayed addition of SP, the flow of mortar for heated and non-heated admixture was decreased. Some researchers reported that the delayed addition of SP resulted in decreased slump values for the period from 5 to 50 minutes after the concrete was mixed with water. But, the fluidity of mortar is affected by different factors like amount and type of admixture, type of cement, and chemical composition of SP. By heat stimulation and the delayed addition of SP, the compressive strength was slightly decreased. Furthermore, by using heat stimulation technique and replacement of cement with slag, the cost of concrete was decreased. II. METHODOLOGY The mixing process was according to the JIS R 5201” Physical testing methods for cement”. The OPC cement was replaced with BFS 30%, 45%, and 60%. Initially, the cement, slag and river sand ware mixed on slow speed of mixer for 30 seconds, subsequently, the water was added and mixed on slow speed for 60 seconds and finally, the mortar was mixed on higher speed of mixer for 30 seconds, with premix of cement BFS and sand. The SP was added to the mix directly with water, and 5 minutes and 10 minutes’ delay. The same procedure was used to prepare the mortar with non-heated SP. The ambient temperature of the mix was 18± 3 °C. To confirm the changes in the fluidity of mortar after heat stimulation of admixture, the flow table of “JIS R 5201” Physical testing methods for cement was used. For the measurement of fluidity, the mortar spread was the average of two perpendicularly crossing diameters by millimeter. Faraidoon Rahmanzai, Mizuki Takigawa, Yu Bomura, Shigeyuki Date Combined Effect of Heat Stimulation and Delayed Addition of Superplasticizer with Slag on Fresh and Hardened Property of Mortar U World Academy of Science, Engineering and Technology International Journal of Structural and Construction Engineering Vol:11, No:10, 2017 1447 International Scholarly and Scientific Research & Innovation 11(10) 2017 scholar.waset.org/1307-6892/10008210 International Science Index, Structural and Construction Engineering Vol:11, No:10, 2017 waset.org/Publication/10008210