Frequently Asked Questions

A Green Portland Cement Alternative, FAQ Friday

You might ask yourself… How is Natural Hydraulic Lime (NHL) a green building material? The simple answer would be that it releases about 80% less CO2, pound for pound when compared to Ordinary Portland Cement (OPC) during the manufacturing process. But why is this so? Well that requires a bit of understanding on the manufacturing of the two very different products.

Both NHL and OPC are made from limestone, although not necessarily the same kinds of stone and are fired in a kiln. NHL is produced in Vertical shaft kilns, which is like a big chimney, with natural gas or clean coal at a low temperature. While OPC is burned in a rotary kiln fired at nearly 2,500 F. The amount fuel used to maintain such a high temperature is by far greater than the relatively low firing temperature of NHL. Often hazardous waste is used as a fuel, which can emit toxins into the atmosphere. During either process CO2 is driven off into the atmosphere. Even though NHL production drives off less CO2, the benefits don’t stop there.

When the NHL is ready to be mixed as a mortar right out of the bag, it’s hungry. NHL wants the CO2 that was pumped into the atmosphere back all for its self, in its natural process to turn back into a limestone. As different grades of NHL are produced their whiteness and density change. On a scale from lightest to heaviest and from whiteness to grayness, NHL 2 is Light and white while OPC in heavy and grey. Since mortar is mixed by volume in the field, less lime is used per pound to make up the same volume of mortar using OPC.

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Originally written by: Randy Ruth
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