Pengaruh campuran bahan additive (bestmittel) dan fly ash terhadap karakteristik beton mutu f’c 25 MPa

The development of the construction sector has driven the need for high-quality concrete that is efficient, economical, and environmentally friendly. One innovation being developed is the partial substitution of cement using fly ash, a byproduct of coal combustion from steam power plants. However, fly ash substitution in concrete work requires a longer setting time and results in lower early strength due to its slower reaction process. To address this, bestmittel is used as an accelerator admixture capable of accelerating concrete hardening at early ages (7-10 days). In this study, the concrete mix design was carried out based on the SNI 03-2834-2000 method with a design compressive strength of 25 MPa. Cement was partially substituted with 10% fly ash by weight of cement, and bestmittel admixture was added with four dosage variaton of 0%, 0,2%, 0,4% and 0,6% of the total cement weight. The tests conducted included compressive strength and modulus of elasticity at the curing ages of 7, 14, and 28 days. The results showed that the substitution of 10% fly ash combined with variations of bestmittel increased the concrete quality as the testing age increased. The optimum value was achieved at a bestmittel dosage of 0,4%, with the highest compressive strength of 28,755 MPa at 28 days, exceeding the design compressive strength of 25 MPa, with an increase from 14 to 28 days of 24,54%. This is attributed to the dosage forming an equilibrium point between accelerated hydration and workability stability, resulting in a denser microstructure. Meanwhile, the 0,6% variation produced a lower compressive strength of 22,533 MPa due to the bestmittel addition exceeding the optimum dosage, causing a more fluid mixture, uncontrolled hydration, and uneven C-S-H formation.