Fast scripted (Winter/ISL), volumetric (UV independent) material mimicking concrete with no finish.

The user can control the tone (bright/dark) with a slider in the albedo shader editor.

All shader editors have a 'Scale' parameter, I recommend setting details small enough so their fractal-ish nature is concealed.

The exponent shader creates a texture-space and time consistent set of reflective points to figure silicates. Switch the shader off if that annoys you, or go Oren-Nayar .