Calcium leaching behavior of cementitious materials in hydrochloric acid solution

Area of Science:

• Materials Science
• Chemical Engineering
• Civil Engineering

Background:

• Cementitious materials are susceptible to chemical attack, particularly from acidic environments.
• Understanding calcium leaching is crucial for predicting the durability and service life of concrete structures.

Purpose of the Study:

• To investigate the calcium leaching behavior of cement paste and silica fume modified calcium hydroxide paste in hydrochloric acid.
• To assess the kinetics of degradation and the impact on material properties.

Main Methods:

• Kinetic analysis via pH changes of hydrochloric acid solution over time.
• Compressive strength testing of specimens after acid exposure.
• Analysis of hydration products using X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TG), and atomic force microscopy (AFM).

Main Results:

• A dynamic equilibrium between calcium hydroxide supply and consumption governs the stability of calcium silicate hydrate (C-S-H).
• Decreased compressive strength correlates with C-S-H decomposition when pore solution calcium hydroxide is below equilibrium concentration.
• The hydration of unhydrated clinker mitigates C-S-H decomposition by increasing pore solution calcium hydroxide.

Conclusions:

• The stability of cement hydration products is critically dependent on the dynamic equilibrium of calcium hydroxide in acidic solutions.
• Acidic environments can lead to significant degradation of cementitious materials, impacting their structural integrity.
• Incorporating silica fume and managing clinker hydration can enhance resistance to acid-induced calcium leaching.