protein from human blood. Scientists demonstrated that such material had compressive strengths as high as 25 MPa, while ordinary concrete had 20–32 MPa. By adding urea (byproduct in urine, sweat, and tears), the resultant material became substantially stronger than ordinary concrete, with 40 MPa of compressive strength. As noted by the authors: Researchers also experimented with synthetic spider silk and bovine serum albumin as regolith binders, noting that these materials could also be produced on Mars after advancements in biomanufacturing technology. The idea behind AstroCrete is not new, that is acknowledged by authors: "adhesives and binders of biological origin were widely utilized by humanity for millennia before the development of synthetic petroleum-derived adhesives. Tree resins, collagen from hooves, casein from cheese, and animal blood were all used as binders and additives for various applications". Researchers calculated that a crew of 6 astronauts could produce over 500 kg of AstroCrete over the course of a two-year mission on the surface of Mars. Each astronaut "could produce enough additional habitat space to support another astronaut, potentially allowing the steady expansion of an early Martian colony". Issues with "Sulfur Concrete" It provides less protection from cosmic radiation, so walls would need to be thicker than concrete walls (the water in concrete is an especially good absorber of cosmic radiation). Sulfur melts at 115.2 °C, and lunar temperatures in high latitudes can reach 123 °C at midday. In addition, the temperature changes could change the volume of the sulfur concrete due to polymorphic transitions in the sulfur. (see Allotropes of sulfur). So unprotected sulfur concrete on the Moon, if directly exposed to the surface temperatures, would need to be limited to higher latitudes or shaded locations with maximum temperatures less than 96 °C and monthly variations not exceeding 114 °C. The material would degrade through repeated temperature cycles, but the effects are likely to be less extreme on the Moon due to the slowness of the monthly temperature cycle. The outer few millimeters may be damaged through sputtering from impact of high energy particles from the solar wind and solar flares. This may however be easy to repair, by reheating or recoating the surface layers in order to sinter away cracks and heal the damage. Use David Bennett, of the British Cement Association, argues that lunarcrete has the following advantages as a construction material for lunar bases: Lunarcrete production would require less energy than