pH Measurement Techniques in Cement-Based Materials

Accurate pH determination in cement-based materials underpins our understanding of hydration kinetics, durability and corrosion risk in reinforced concrete. Fresh cement pastes and hardened mortars exhibit highly alkaline pore solutions (pH 12–13.5) owing to the dissolution of portlandite and alkali species. Over time, processes such as carbonation, leaching and chloride ingress reduce alkalinity, compromising steel passivation. Measurement approaches fall broadly into ex-situ and in-situ methods. Ex-situ techniques extract pore solution by mechanical pressing, vacuum filtration or by leaching powdered samples in a controlled solvent ratio. Sample preparation variables—particle size, drying conditions, solid-to-solvent ratio and atmospheric exposure—profoundly influence results. In-situ monitoring employs optical probes (luminescent dyes or fibre-optic sensors), microelectrodes and capacitive devices to track pH evolution during early hydration or carbonation with high temporal resolution. Advances in sensor design now permit continuous recording of pH changes in slurries, pastes and hardened matrices, enabling direct correlation with heat release, solid phase transformations and ingress front progression. Selection of the most appropriate technique hinges on the stage of material, required spatial and temporal resolution, cost constraints and compatibility with field or laboratory environments. Reliable pH data inform global efforts in structural health monitoring, forensic analysis and design of tailored mineral admixtures to enhance service life.

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Research from all publishers

Recent work has demonstrated the power of optical luminescent sensors for in-situ pH tracking during early hydration. These sensors, embedded in cementitious slurries, record pH every few seconds over extended periods, resolving the alkali release and Ca(OH)₂ consumption in various cement chemistries and correlating these profiles with calorimetric data. Complementary studies have refined the ex-situ leaching method to establish a standardized procedure that minimises air exposure, controls specimen dryness and powder size, and maintains solution temperature—yielding highly reproducible pH measurements across laboratories. Investigations into particle-size effects reveal that coarse fragments (600 µm–4.75 mm) can substitute fine powders (<600 µm) in leaching protocols, provided the solid-to-solvent ratio or contact time is adjusted, thus reducing sample preparation costs without sacrificing accuracy.

pH Measurement Techniques in Cement-Based Materials publication trend

The graph below shows the total number of articles in ph measurement techniques in cement-based materials across all publications each year (not limited to Nature Index journals).

Technical terms

pH: Negative logarithm of hydrogen ion activity, indicating solution acidity or alkalinity.

Pore solution: The aqueous phase occupying capillary and gel pores within cementitious materials.

Ex-situ leaching method: Procedure to extract soluble species by immersing powdered cementitious material in a defined solvent for subsequent pH analysis.

In-situ monitoring: Real-time measurement of pH within the material matrix using embedded sensors without extracting pore fluid.

Solid-to-solvent ratio: Mass ratio of powdered sample to liquid in leaching experiments, affecting ion concentration and measured pH.

Luminescent sensor: Optical probe containing pH-sensitive dyes that emit light at wavelengths proportional to local pH.

References

1. A review of sample preparation and its influence on pH determination in concrete samples. Materiales de Construcción (2017).
2. Continuous optical in-situ pH monitoring during early hydration of cementitious materials. Cement and Concrete Research (2021).
3. Standardized Procedure of Measuring the pH Value of Cement Matrix Material by Ex-Situ Leaching Method (ESL). Crystals (2021).
4. pH Measurement of Cement-Based Materials: The Effect of Particle Size. Applied Sciences (2021).
5. Real-Time Monitoring of Cement Paste Carbonation with In Situ Optical Fiber Sensors. Chemosensors (2023).