I wanted to make some plain, flat bases more interesting, so I gave this a try. I kinda like it and I hope someone finds it useful.

Cement

1. Basecoat with 50-50 Mechanicus Standard Grey and Abaddon Black .
2. Stiple and drybrush Dawnstone over the majority of the base.
3. Now take Administratum Grey and repeat the steps above. Do this over a smaller area, but within the previously established texture.
4. Add a little white to your Administratum Grey and pop a few addition scratches and dings here and there. Use a fine brush and try to keep lines and dots as thin as possible.

Cracks

1. Take Abaddon Black and plot out some cracks. Make the lines vary in thickness and be wavy. It is also a good idea to create chips and small holes by dabbling the tip of your brush in small odd shaped patches.
2. With Administratum Grey , highlight the inside of the curves of your black lines. Make these lines thicker in the middle.
3. Add some pure white to the Administratum Grey and add smaller highlights to the thicker parts of the last stage. Make these more selective and place them right where the black and grey meet.