Test service for alkali resistance and strength retention rate

Alkali Resistance and Strength Retention Testing Service – Comprehensive Evaluation of Material Durability in Alkaline Environments

As an ISO/IEC 17025 accredited independent testing laboratory, we offer specialised alkali resistance and strength retention testing services to manufacturers, engineering contractors, and quality assurance teams across the construction, chemical processing, pulp and paper, textile, and protective coatings sectors. Alkaline environments – ranging from concrete and mortar (pH 12-13), to caustic soda solutions, and to alkaline process streams – can cause severe degradation of materials, including chemical attack, dissolution, swelling, cracking, and loss of mechanical properties. Our alkali resistance test protocols evaluate the resistance of metals, polymers, composites, coatings, textiles, and building materials to alkaline media under controlled temperature and concentration conditions. The strength retention rate – the percentage of original strength maintained after exposure – provides a direct measure of the material's durability and fitness for service. All methods are aligned with ISO, ASTM, EN, and GB standards, including ISO 175 (Plastics – Determination of the effects of liquid chemicals), ASTM D543 (Resistance of plastic materials to chemical reagents), ISO 10545-13 (Ceramic tiles – Determination of chemical resistance), ASTM C267 (Chemical resistance of mortars, grouts and monolithic surfacings), and GB/T 11547 (Determination of the effects of liquid chemicals on plastics). Our reports are recognised by national regulatory authorities, international certification bodies, and major industry buyers for product qualification, type approval, and quality assurance.

Materials and Products We Regularly Test

Our alkali resistance laboratory accommodates a wide range of materials, coatings, and finished products. Typical test articles include:

Polymer materials – thermoplastics (PVC, PE, PP, PA, PEEK), thermosets (epoxy, polyester, vinyl ester), and elastomers (EPDM, NBR, FKM, silicone)
Fibre-reinforced composites – glass fibre reinforced plastics (GRP), carbon fibre composites, and hybrid composites for chemical process equipment
Protective coatings and linings – epoxy, polyurethane, vinyl ester, and rubber linings for tanks, pipes, and concrete structures
Construction materials – concrete, mortar, cementitious grouts, and ceramic tiles
Textiles and fibres – natural fibres (cotton, wool), synthetic fibres (polyester, nylon, aramid), and coated fabrics
Metals and alloys – stainless steels, aluminium alloys, nickel-based alloys, and copper alloys
Glass and ceramics – borosilicate glass, soda-lime glass, and ceramic coatings
Gaskets, seals and adhesives – elastomeric seals, structural adhesives, and sealants

Alkali Resistance Test Methods – Immersion and Exposure Protocols

Total immersion test – ISO 175 / ASTM D543 / GB/T 11547 – for plastics, composites and elastomers – We immerse test specimens (typically 50 mm × 50 mm or larger) in a specified alkaline solution (e.g., 5 % NaOH, 10 % NaOH, 20 % NaOH, or saturated Ca(OH)₂) at a controlled temperature (typically 23 °C, 40 °C, 60 °C, or 80 °C) for a specified period (typically 7, 14, 28, or 56 days). The solution is maintained at the specified concentration by periodic replenishment. After exposure, we evaluate the specimens for changes in weight, dimensions, appearance, and mechanical properties (tensile, flexural, or compressive strength).
Spot test (drop test) – ISO 10545-13 / ASTM D543 – for coatings, ceramics and glazed surfaces – We apply a drop of the alkaline test solution (e.g., 10 % NaOH or 20 % NaOH) to the surface of the test specimen and cover it with a watch glass to prevent evaporation. The specimen is maintained at a controlled temperature (typically 23 °C or 40 °C) for a specified period (typically 24-72 hours). After exposure, we rinse the surface and evaluate it for changes in colour, gloss, surface texture, blistering, or loss of adhesion.
Alternate immersion (wet/dry cycling) – for simulating service conditions with wetting and drying cycles – We cycle the specimen between immersion in the alkaline solution and exposure to air (drying) to simulate the wetting and drying cycles experienced by materials in service (e.g., concrete structures, chemical plant equipment). The cycle frequency (e.g., 4 hours immersed, 20 hours dry) and the number of cycles (typically 10-100) are selected to match the expected service conditions.
Pressurised alkaline exposure – for simulating deep-well and high-pressure process conditions – For components used in high-pressure alkaline environments (e.g., oil and gas production, chemical reactors), we perform exposure testing in a pressurised autoclave at elevated pressures (up to 10 MPa) and temperatures (up to 150 °C). The test conditions are selected to match the service environment, and the specimens are evaluated for degradation and strength retention.
Alkali spray and fog testing – ASTM B117 (modified) – for assessing surface degradation under alkaline mist – We expose the test specimen to a fine alkaline spray (or fog) in an environmental chamber at a specified temperature and concentration. The test is used to simulate the exposure of outdoor structures to alkaline dust or to alkaline mist from process equipment.

Strength Retention Rate – Quantifying the Loss of Mechanical Properties

Mechanical property testing before and after alkali exposure – ISO 527 / ISO 178 / ASTM D638 / ASTM D790 – We perform tensile, flexural, or compressive strength tests on a set of unexposed (control) specimens and on a set of exposed specimens. The strength retention rate is calculated as the percentage of the original strength retained after exposure: Retention (%) = (Strength_exposed / Strength_unexposed) × 100. A retention rate of ≥ 80 % is generally considered acceptable for most structural applications; for critical applications, a retention rate of ≥ 90 % may be required.
Hardness retention – ASTM D2240 / ISO 7619-1 – for elastomers and rubbers – We measure the Shore hardness (Shore A or Shore D) of the specimen before and after alkali exposure. The hardness retention rate is calculated and used to assess the degree of softening (or hardening) caused by the alkaline environment.
Weight and dimensional change – for assessing chemical attack and swelling – We measure the weight and the dimensions (length, width, thickness) of the specimen before and after exposure. A weight gain > 5 % or a dimensional change > 2 % typically indicates significant chemical attack (swelling, absorption, or surface degradation).
Surface hardness and abrasion resistance – after alkali exposure – For coated surfaces, we measure the surface hardness (by pencil hardness, Taber abrasion, or other methods) before and after alkali exposure to assess the degradation of the protective coating.

Material-Specific Alkali Resistance – Plastics, Composites, Coatings and Construction Materials

Alkali resistance of plastics and composites – ISO 175 / ASTM D543 – We test the resistance of plastics and composites to caustic soda (NaOH), potassium hydroxide (KOH), and calcium hydroxide (Ca(OH)₂) solutions at various concentrations and temperatures. The test evaluates the resistance to hydrolysis, swelling, stress cracking, and loss of mechanical properties – critical for materials used in chemical processing equipment, pipes, and storage tanks.
Alkali resistance of protective coatings and linings – ASTM C267 / NACE TM0293 – We evaluate the resistance of protective coatings (epoxy, polyurethane, vinyl ester, rubber linings) to alkaline solutions. The test assesses the coating for blistering, loss of adhesion, softening, and failure. A coating that passes the test must show no blistering, adhesion loss, or significant softening after exposure.
Alkali resistance of concrete and cementitious materials – ASTM C267 / EN 13510 – We test the resistance of concrete, mortar, and grout to alkaline attack (e.g., from alkaline groundwater, leaching, or chemical processes). The test measures the compressive strength retention, weight change, and dimensional stability of the material after exposure.
Alkali resistance of glass and ceramics – ISO 10545-13 / ASTM C150 – For ceramic tiles, glass, and glazed surfaces, we test the resistance to alkaline staining and surface attack. The test assesses the gloss change, colour change, and surface roughness of the material after exposure.
Alkali resistance of metals – ASTM G31 / ISO 11114 – for metallic materials in caustic environments – We measure the corrosion rate (in mm/year) and the pitting susceptibility of metals (stainless steels, aluminium, nickel alloys) in alkaline solutions. The test is performed under controlled temperature and concentration, and the corrosion rates are compared to the maximum allowable limits for the application.

Environmental Conditioning and Ageing – Assessing Long-Term Durability

Accelerated alkali ageing – at elevated temperatures (e.g., 60 °C, 80 °C) – We perform accelerated ageing tests by exposing the material to a higher temperature (e.g., 60 °C or 80 °C) while immersed in the alkaline solution. The test duration is reduced by using the Arrhenius equation to estimate the equivalent exposure time at the service temperature.
Thermal cycling during alkali exposure – for simulating diurnal and seasonal temperature changes – We cycle the temperature (e.g., 20 °C to 60 °C) while the specimen is immersed in the alkaline solution. The thermal cycling accelerates the degradation by creating cyclic stresses on the material.
Combined alkali and mechanical loading (stress corrosion cracking) – ASTM G36 / NACE TM0177 – For materials that are exposed to alkaline solutions under tensile stress, we perform stress corrosion cracking (SCC) testing using U-bend, C-ring, or four-point bent beam specimens. The test determines the susceptibility of the material to alkaline stress corrosion cracking.
Humidity and condensation after alkali exposure – for assessing post-exposure performance – After the alkali exposure, we condition the specimens in a humidity chamber (e.g., 95 % RH, 40 °C) to assess the effect of moisture on the degraded material.

Data Analysis and Interpretation – Quantifying Alkali Resistance

Strength retention rate – the primary indicator of durability – The strength retention rate (in %) is the key output of the alkali resistance test. A retention rate of ≥ 80 % is generally considered acceptable, while a retention rate of ≥ 90 % is required for critical applications. We provide a clear statement on whether the material meets the specified retention requirement.
Weight change and dimensional stability – for assessing chemical attack – Weight gain (due to absorption or chemical reaction) and dimensional changes (swelling, shrinking, or cracking) are reported and correlated with the loss of mechanical properties.
Visual assessment – colour change, gloss change, blistering, and cracking – ISO 4628 / ASTM D714 – We provide a detailed visual assessment using standard rating scales for blistering (ASTM D714), rusting (ASTM D610), and cracking (ISO 4628). The results are documented with high-resolution photographs.
Statistical analysis – for batch-to-batch consistency – For multiple specimens, we report the mean, standard deviation, and coefficient of variation (CV) for the strength retention rate and other parameters. A CV of less than 10 % indicates excellent batch-to-batch consistency.

Regulatory Compliance and Product Certification – Supporting Industry Standards

Our alkali resistance and strength retention testing services are performed in accordance with a wide range of national and international standards. The most commonly requested include:

ISO 175 – Plastics – Determination of the effects of liquid chemicals – the international standard for chemical resistance testing of plastics
ASTM D543 – Standard Test Methods for Resistance of Plastic Materials to Chemical Reagents – the North American standard for chemical resistance
ISO 10545-13 – Ceramic tiles – Determination of chemical resistance – for ceramic tiles
ASTM C267 – Standard Test Methods for Chemical Resistance of Mortars, Grouts, and Monolithic Surfacings – for cementitious materials
NACE TM0293 – Standard Test Method for the Determination of the Resistance of Coatings to Chemical Attack – for protective coatings
GB/T 11547 – Determination of the effects of liquid chemicals on plastics – the Chinese national standard for chemical resistance
ASTM G31 – Standard Guide for Laboratory Immersion Corrosion Testing of Metals – for metallic materials
ISO 11114 – Metallic materials – Corrosion tests – General principles for testing in liquid media – for metals

Report Acceptance and Regulatory Recognition

All alkali resistance and strength retention tests are conducted under our ISO/IEC 17025 accreditation, using calibrated environmental chambers, immersion baths, and mechanical testing machines, all traceable to national and international reference standards. Our final test reports include: a complete description of the test article (material, dimensions, manufacturer), the test method and conditions (alkali concentration, temperature, exposure time, pressure), the measured parameters (strength retention rate, weight change, dimensional change, visual rating), the statistical summary (mean, standard deviation, CV), and a clear pass/fail verdict against your specified acceptance criteria. These reports are accepted by the National Medical Products Administration (NMPA), the State Administration for Market Regulation (SAMR), the Ministry of Industry and Information Technology (MIIT), and international certification bodies for product registration, type approval, and quality assurance. Bilingual (Chinese/English) versions are available to facilitate submissions to domestic and international authorities and to support your global market access.