Analisis Kuat Tarik Belah Beton Padat Gilas Dengan Terak Nikel Sebagai Substitusi Agregat Kasar Sebanyak 25%, 50%, dan 75% Menggunakan Ultrasonic Pulse Velocity dan Digital Image Correlation Menurut ASTM C496 dan BS EN 12390-6 = Analysis of the Split Tensile Strength of Roller-Compacted Concrete with 25%, 50%, and 75% Coarse Aggregate Substitution Using Nickel Slag Evaluated by Ultrasonic Pulse Velocity and Digital Image Correlation According to ASTM C496 and BS EN 12390-6