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.

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This study aims to determine the physical properties and quality of the concrete block that contain palm ash as a partial replacement of cement.The sample of concrete blocks measuring 40x20x10 cm with compositions 1 cement and 4 sand (volume ratio).Variations of the test specimen without palm ash and containing palm ash content with 5%, 10%, 15%, and 20% of the cement used.The test includes examining the size, the compressive strength testing, and water absorption.The test results showed that the length and width of the concrete blocks are still in the allowable limits, but the thickness does not meet standards. The results of compressive strength testing of concrete blocks with ash content 5%, 10%, and 15% are considered quality II, concrete blocks without ash and with ash content of 20% included in the quality III. The test results of water absorption for all variations of the mixture into the quality I and II Keywords: concrete block, palm fiber, measure, strength, water absorption  ABSTRAK Penelitian ini bertujuan untuk mengetahui sifat-sifat fisis dan mutu batako akibat adanya abu sabut kelapa sawit (SKS) sebagai bahan pengganti sebagian semen. Benda uji berupa batako berukuran 40x20x10 cm dengan komposisi 1 semen dan 4 pasir (perbandingan volume). Variasi benda uji yakni batako tanpa abu SKS, dan batako dengan abu SKS sebesar 5%, 10%,15%, serta 20% dari kebutuhan semen. Pengujian meliputi pemeriksaan ukuran, pengujian kuat tekan, dan penyerapan air. Hasil pemeriksaan ukuran menunjukkan bahwa panjang dan lebar batako masih berada dalam batas yang diperkenankan, tetapi tidak demikian dengan tebal batako. Hasil pengujian kuat tekan batako dengan kadar abu 5%, 10%, dan 15% masuk dalam mutu II, sedangkan batako tanpa kadar abu dan batako dengan kadar abu 20% masuk dalam mutu III (Balitbang Kimpraswil, 2003b). Hasil pengujian penyerapan air untuk semua variasi campuran masuk dalam mutu I dan II (Balitbang Kimpraswil, 2003b). Kata kunci: batako, sabut kelapa sawit, ukuran, kuat tekan, penyerapan air.