Quikrete. Green Concrete Mix comprises 50% recycled material, including recycled aggregates, fly ash, and/or slag cements, diverting 0.25 cubic feet of waste from landfills per 60-pound bag of material, according to the firm. The material achieves a compressive strength of 3,500 psi in 28 days, meeting ASTM C 387 performance requirements. It is suitable for general concrete work. 800.282.5828. www.quikrete.com.