High Early Compressive Strength Concrete Berbasis Kombinasi Semen OPC dan Ground Granulated Blast Furnace Slag dengan Alkali Aktivator dan Superplasticiser
Elvina Juesmin, Alkali Activator, Ground Granulated Blast Furnace Slag, High Early Strength, Portland, Superplasticizer
2025 | Tesis | S2 Teknik Sipil
Di tengah tuntutan dunia konstruksi yang semakin cepat dan efisien, beton dengan kekuatan awal tinggi menjadi pilihan penting. Beton berkekuatan awal tinggi dituntut mampu mencapai kuat tekan minimum 20 MPa dalam 24 jam. Namun, pencapaian ini umumnya memerlukan peningkatan jumlah semen, yang berdampak pada emisi karbon dan biaya produksi. Untuk menguranginya, semen dapat disubstitusi dengan pozzolan seperti GGBFS (Ground Granulated Blast Furnace Slag) yang memiliki komposisi kimia mirip semen. Meski demikian, GGBFS memiliki proses hidrasi yang lambat sehingga dibutuhkan alkali aktivator untuk mempercepat reaksi. Di sisi lain, aktivasi alkali dapat menurunkan workabilitas, sehingga diperlukan penambahan admixture seperti superplasticiser agar kelecakan tetap terjaga. Penelitian ini mengkaji pengaruh penambahan alkali aktivator dan superplasticiser terhadap kuat tekan awal dan workabilitas dengan substitusi GGBFS. Penelitian ini bertujuan mengembangkan beton kuat awal tinggi yang lebih ramah lingkungan dengan target kuat tekan 20 Mpa dalam 24 jam dan nilai slump 18-20 cm.
Perancangan campuran menggunakan metode volume absolut. Pengujian pasta dan mortar berupa flow table dan kuat tekan pada umur 24 jam. Pengujian beton berupa uji slump dan kuat tekan dengan spesimen silinder 100x200 mm pada umur 24 jam. Semen OPC dan GGBFS digunakan dengan rasio (90:10; 80:20; 70:30). Alkali aktivator terdiri dari NaOH dan Na?SiO?, dengan rasio Na?SiO?/NaOH (R) sebesar 1.5 dan rasio total alkali terhadap GGBFS (A) sebesar 0.45. Superplasticiser yang digunakan adalah Sika® ViscoCrete®-1050 HE dengan dosis 0.5?n 1%. Variasi aktivator alkali yang diuji yaitu 0%, 2.5%, 5%, 7.5%, dan 10%. Rasio volume pasta terhadap rongga agregat halus (Rm) yaitu 1.4, 1.5, dan 1.6.Volume mortar terhadap rongga agregat kasar (Rb) ditetapkan 1.4.
Penggunaan superplasticiser dalam campuran dapat meningkatkan flowability. Pada pencampuran tanpa menggunakan superplasticiser nilai flow pada campuran 30% hanya 51%. Sedangkan pada penambahan 0.5?n 1.0% superplasticiser, nilai flow mencapai maksimum yaitu 160%. Penambahan alkali aktivator pada beton dapat meningkatkan kuat tekan pada umur awal. Kuat tekan meningkat seiring dengan bertambahnya persentase alkali aktivator. Pada campuran beton tanpa menggunakan alkali aktivator kuat tekan beton yaitu 31.9 MPa, sedangkan pada penambahan 10% aktivator kuat tekan meningkat hingga 34.66% yaitu 43 MPa. Akan tetapi, perlu diperhatikan bahwa penambahan alkali aktivator dalam jumlah yang tinggi dapat menurunkan workabilitas pada beton. Komposisi optimum pada penelitian ini terhadap kemudahan dalam pengerjaan (workability) dan kuat tekan terdapat pada substitusi 30% GGBFS pada semen OPC dengan 0.5% superplasticiser dan 5% alkali aktivator. Dimana kuat tekan yaitu 34.5 MPa dan nilai slump 19.5 cm.
In the midst of the construction industry's demand for faster and more efficient processes, high early strength concrete has become an important choice. High early strength concrete is required to achieve a minimum compressive strength of 20 MPa within 24 hours. However, achieving this typically requires an increase in the amount of cement used, which impacts carbon emissions and production costs. To mitigate this, cement can be substituted with pozzolans such as GGBFS (Ground Granulated Blast Furnace Slag), which has a chemical composition similar to cement. However, GGBFS has a slow hydration process, so an alkali activator is needed to accelerate the reaction. On the other hand, alkali activation can reduce workability, so the addition of admixtures such as superplasticizers is necessary to maintain workability. This study investigates the effect of adding alkali activators and superplasticizers on early compressive strength and workability with GGBFS substitution. The aim of this study is to develop high-early-strength concrete that is more environmentally friendly, targeting a compressive strength of 20 MPa within 24 hours and a slump value of 18–20 cm.
The mix design uses the absolute volume method. Tests on paste and mortar include flow table tests and compressive strength at 24 hours. Concrete tests include slump tests and compressive strength tests using 100x200 mm cylindrical specimens at 24 hours. OPC cement and GGBFS are used in ratios of (90:10; 80:20; 70:30). The alkali activator consists of NaOH and Na?SiO?, with a Na?SiO?/NaOH ratio (R) of 1.5 and a total alkali-to-GGBFS ratio (A) of 0.45. The superplasticizer used is Sika® ViscoCrete®-1050 HE at a dosage of 0.5% and 1%. The alkali activator variations tested were 0%, 2.5%, 5%, 7.5%, and 10%. The paste-to-fine aggregate void ratio (Rm) was 1.4, 1.5, and 1.6. The mortar-to-coarse aggregate void ratio (Rb) was set at 1.4.
The use of superplasticizers in the mixture can improve flowability. In mixtures without superplasticizers, the flow value at 30% was only 51%. However, with the addition of 0.5% and 1.0% superplasticizers, the flow value reached a maximum of 160%. The addition of alkali activators to concrete can increase compressive strength at early ages. Compressive strength increases with the percentage of alkali activator. In concrete mixtures without alkali activator, the compressive strength is 31.9 MPa, while with the addition of 10?tivator, the compressive strength increases to 34.66%, or 43 MPa. However, it should be noted that the addition of high amounts of alkali activator can reduce the workability of the concrete. The optimal composition in this study for workability and compressive strength was achieved by substituting 30% GGBFS for OPC cement with 0.5% superplasticizer and 5% alkali activator. The compressive strength was 34.5 MPa, and the slump value was 19.5 cm.
Kata Kunci : Alkali Aktivator, Ground Granulated Blast Furnace Slag, High Early Strength, Portland, Superplasticiser
