Making durable blocks from silt?

I was planning of doing some experiments in making exterior patio pavers using my native soil (giles silt loam probably less than 20% clay or sand). 

I am in a very humid mild climate, and so I think an adobe type thing would turn to mush. 

I was planning on seeing how far I could stretch portland cement and still get something durable... or maybe add sand (more locally available for less energy) to further stretch the function of the cement?

Any thoughts, experience, or alternatives?

PRC

at work when we make stucco  its 5-1 ratio by weight  100 lb portland 500 lb sand