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The goal of this research is to investigate the influence of seawater as mixing water and curing water on characteristics of cement paste and mortar. Research was conducted with making mixtures of cement paste and mortar using two kind of cement, Portland Composite Cement (PCC) and Pozzolana Portland Cement (PPC) with seawater as mixing water. Characteristics of fine aggregate and characteristics of cement paste with seawater mixing were investigated. Furthermore, 144 cube mortar specimens in size of 5 cm x 5 cm x 5 cm in four series mortar mixtures were casted according with SNI 03-6825-2002. At 24 hours after specimens were casted, cube mortar specimens were cured in tap water curing (TC), seawater curing (SC) and air curing (AC). After achievement at certain curing day of 3, 7, 14 and 28 days, cube mortar samples were tested in compressive strength. Results concluded that seawater mixing improves compressive strength of mortar up to 28 days in all curing conditions, TC, SC and AC. Moreover, strength of mortar is not affected by type of curing water, tap water or seawater.

This present paper aims to investigate strength characteristics of cement mortar using natural sea sand as fine aggregate in different curing conditions. Research was carried out with making mortar mixtures by two types of cement, Portland Composite Cement (PCC) and Pozzolana Portland Cement (PPC) with tap water as mixing water. Characteristics of fine aggregate and strength of cement mortar use river sand (RS), sea sand (SS), and washed sea sand (WS) were observed. Further, specimens of cube mortar in size of 50 mm x 50 mm x 50 mm of six mortar mixture series were casted according to Indonesian Standard. At 24 hours after cube specimens were casted, cube mortar specimens were cured in three curing conditions such as tap water curing (TC), seawater curing (SC) and air curing (AC). After curing at certain period (3-day, 7-day, 14-day, and 28-day), cube mortar samples were tested in compressive strength. Results concluded that sea sand aggregate improve characteristic of mortar in compressive strength up to 28 days in all curing conditions, and there was no significant effect of type of curing water (TC and SC) on 28-day strength performance of mortar was obtained. In addition, sea sand could potentially be utilized as an aggregate in production of mortar and/or concrete.