Hello. I am almost done laying the block for the retaining wall for my crawlspace-to-basement conversion project. Naturally, I need to fill the cores that have rebar. However, I am having a tough time finding that product. The local big box home stores don't carry it and the concrete place I've been buying block from only sells the portland cement - not the premixed core-fill grout. Can I just use regular concrete to do the job? I'm filling the cores for standard 2-core 8" block with #4 rebar running through it so it is not really a tight squeeze if that is relevant. Thanks.