Building Materials: Introduction to Hydraulic Lime

Building Materials: Introduction to Hydraulic Lime

Key words

Hydraulic lime, NHL2, NHL5, NHL3.5, ancient building restoration, lime, traditional building restoration

Overview

Hydrated lime can be divided into two categories: gas-hardening lime (calcium Lime) and hydraulic lime. Hydraulic lime was discovered and invented by Europeans and is common in Europe and other countries around the world, but rarely in China.

European description of hydraulic lime: "Slaked lime obtained by firing and digesting clay limestone with varying clay content or siliceous limestone with varying silica content, or by mixing calcium silicate, calcium aluminate Lime obtained from calcium hydroxide. Its characteristics are that it hardens after contacting with water, and then carbonizes in the air to develop strength, and can maintain and continue to develop strength in water. It is mainly used as a cementing material to make buildings. used for bonding, plastering or pointing mortar.”

Application

Various types of repairing agents, caulking agents, grouting adhesives, etc., which are specially used for masonry building repairs, using hydraulic lime as raw materials.

Almost all masonry monuments and historical buildings use lime materials as the base material for restoration, or use (hydraulic) lime materials added with active hydraulic components, and only 3% of traditional air-setting lime is used for building materials.

Lime Classification

Hydraulic lime is divided into natural hydraulic lime (Natural Hydraulic Lime) and artificial hydraulic lime (Hydraulic Lime).

Natural hydraulic lime: slaked lime obtained by firing and digesting clay limestone with a clay content of 15-20% or siliceous limestone with a silica content of about 13%;

Artificial Hydraulic Lime: Lime obtained by mixing substances containing calcium silicate, calcium aluminate and calcium hydroxide.

Classification

NHL is divided into three levels: NHL2, NHL3.5 and NHL5

Performance advantage

It has hydraulic hardness, fast setting speed, good viscosity, strong adhesion, high water resistance, and high mechanical strength; compared with cement, it has air hardness, which can make the wall breathable, keep breathing, and is conducive to the exchange of water vapor. It has the characteristics of good frost resistance and alkali resistance, good flexibility, good machinability, and strong self-healing ability.

Due to the low hydration exotherm and gas-hardening anti-exothermic heat, the internal stress caused by rapid curing is avoided and it has good toughness.

Based on the requirements of cementitious materials for preservation and maintenance of ancient buildings or traditional buildings: that is, the restoration materials should match the original materials. This is an important advantage of hydraulic lime.