San Jose Mercury News: Brent Constantz’s last startup, Skeletal Kinetics, created a bone-fracture cement that costs $200 per gram and helps orthopedic surgeons heal their patients. His new startup aims to churn out billions of tons of market-price construction cement that Constantz says can help heal planet Earth by embedding billions of tons of greenhouse gases into concrete. And it will deliver desalinated water as a byproduct. Constantz is founder and CEO of Calera, a 3-year-old Los Gatos-based …