Abstract.One of the limitations of geopolymer as the alternative binders in concrete is the necessity of heat curing. This study aimed to produce fly ash geopolymer binder subjected to ambient curing by adding a small proportion of lime and varying the activator dosage. The Class F fly ash from Mpanau coal-fired power plant was mixed with alkaline solution consists of sodium silicate and sodium hydroxide with Na2O dosage of 5%, 7%, and 9%. To achieve ambient cured paste, 8%, 9%, and 10% slaked lime was added as the substitute for the fly ash. The setting time test was conducted for each mix and the compressive strength was performed at age of 7, 14 and 28 days. The test result shows that the setting time of the fly ash based geopolymer paste can be controlled by adding a small proportion of slaked lime. The addition of lime increased strength but decreased the setting time.

Coarse aggregate is the dominant constituent in concrete. Aggregate hardness is a variable needed to investigate in determining its effect on the critical stress intensity factors (KIC), dissipated fracture energy (Gf) and compressive strength (fc’) of the concrete. The hardness of coarse aggregate based on Los Angeles abrasion values of 16.7%., 22.6%, and 23.1% was used incorporated with Portland Composite Cement (PCC), and superplasticizer to create specimens. Cubes of 150x150x150 mm were employed to determine the fc’, and four beam sizes: 50x100x350 mm, 50x150x500 mm, 50x300x950 mm and 50x450x1250 mm were engaged to determine KIC and Gf. The fc’ and Gf of specimens manufactured by three different hardness of coarse aggregates were 45, 43, 40 MPa and 89.4, 54.0, 56.3 N/m respectively. KIC of specimens was 138.9, 119.4 and 114.1 MPa.mm1/2 for beam size of 50x100x350 mm; 148.2, 115.8 and 108.8 MPa.mm1/2 for beam size of 50x150x500 mm; 230.9, 183.1 and 157.9 MPa.mm1/2 for beam size of 50x300x950 mm; and 293.2, 248.1 and 244.3 MPa.mm1/2 for beam size of 50x450x1250 mm. Experimental results showed that decreasing hardness of coarse aggregate was found to have significant effect on the fracture toughness rather than on the compressive strength of concrete.

AbstrakStandar Nasional Indonesia (SNI) nomor 03-2834-2000 (SNI 03-2834-2000) memberikan empat jenis slope gradasi gabungan agregat kasar dan halus dalam pembuatan beton  normal. Investigasi empat jenis slope gradasi agregat gabungan ini akan dilakukan untuk mengetahui pengaruhnya terhadap kuat tekan dan fracture toughness dari beton. Material dasar penyusun beton yang berasal dari Sungai Palu dan memenuhi kriteria standar SNl yang dipakai dalam membuat benda uji. Uji kuat tekan beton digunakan kubus berdimensi 150x150x150 mm dalam menentukan nilai kuat tekan beton (fc'), dan empat jenis balok berdimensi tebal, tinggi dan panjang: 50 x 100 x 300 mm, 50 x 150 x 450 mm, 50 x 300 x 900 mm, dan 50 x 400 x 1200 mm untuk uji Three-Point Bend (TPB) dalam menentukan fracture toughness beton (KIC). Hasil investigasi ini menunjukan bahwa gradasi agregat gabungan yang dipakai dalam campuran beton akan berpengaruh tidak signifikan pada nilai fc', akan tetapi berpengaruh signifikan pada nilai  KIC.AbstractIndonesian National Standard 03-2834-2000 (SNI 03-2834-2000) proposed four types of combined aggregate grading of coarse and fine aggregates in designing normal concrete strength. Investigation of four combined aggregate grading types was performed to determine its effect on the compressive strength and fracture toughness of the concrete.Basic material constituents of concrete were used from Palu river and fulfilling SNI criteria in manufacturing samples. Cubes of 150x150x150 mm were used to determine concrete compressive strength value (fc'), and four types of beams with dimension of width, height, and length: 50 x 100 x 300 mm, 50 x 150 x 450 mm, 50 x 300 x 900 mm, dan 50 x 400 x 1200 mm for Three-Point Bend (TPB) test method to determine fracture toughness of the concrete (KIC). Current research results were found that combined aggregate grading types influenced insignificantly on the fc' value, but significantly on the KIC value.