The utilization of fly ash as sand partial replacement in concrete mix is an alternative solution for the depletion of sand resources in the Special Region of Yogyakarta. This research evaluates the effect of sand partial replacement with fly ash to the strength-weight and cost-strength ratio of concrete mixes. The strength-weight ratio was used for mechanical evaluation with higher value considered as better, while cost-strength ratio indicates its economic efficiency with lower value means more efficient. Four groups of test specimens with different amounts of fly ash were evaluated for its mechanical performance and economic efficiency. Various percentages of fly ash, sequentially 0%, 20%, 35%, and 50% were implemented in the mixes based on partial weight replacement of its components and the water-binder ratios were calculated based pozzolanic cementing efficiency method. The compressive strength was evaluated on 14 concrete cylinders with 150mm diameter and 300mm length for each variant that cured in 28 days water immersion. Test results shows that fly ash addition tend to reduce material cost and density of concretes, yet the compressive strength was not lower compared to normal concrete. Therefore, fly ash added concrete can be justified as better in mechanical performance and economically more efficiency.

利用粉煤灰作为混凝土混合物中的砂子部分替代物是日惹特区砂子资源枯竭的替代解决方案。本研究评估了用粉煤灰部分替代沙子对混凝土混合料强度重量比和成本强度比的影响。强度重量比用于力学评价，数值越高越好，成本强度比表明其经济性，数值越小越有效。对四组不同粉煤灰量的试件进行力学性能和经济效益评价。不同百分比的飞灰，依次为 0%、20%、35%、和50%的混合料基于其组分的部分重量替换和水胶比基于火山灰固井效率法计算。在 14 个直径为 150 毫米、长度为 300 毫米的混凝土圆柱体上评估了在 28 天的水中浸泡固化的每个变体的抗压强度。试验结果表明，添加粉煤灰有助于降低混凝土的材料成本和密度，但与普通混凝土相比，其抗压强度并没有降低。因此，可以证明添加粉煤灰的混凝土具有更好的机械性能和更经济的效率。试验结果表明，添加粉煤灰有助于降低混凝土的材料成本和密度，但与普通混凝土相比，其抗压强度并没有降低。因此，可以证明添加粉煤灰的混凝土具有更好的机械性能和更经济的效率。试验结果表明，添加粉煤灰有助于降低混凝土的材料成本和密度，但与普通混凝土相比，其抗压强度并没有降低。因此，可以证明添加粉煤灰的混凝土具有更好的机械性能和更经济的效率。