Alkali-resistant Mesh Cloth Testing

Alkali-resistant mesh fabric inspection mainly conducts scientific testing and analysis on the key performance indicators, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Core Testing Items

Mass per unit area: This is the basic indicator for evaluating whether the material usage of the alkali-resistant mesh fabric is sufficient and for assessing the influence on the physical properties. The testing method usually follows GB/T 9914.3 or the relevant standards, calculating by precisely weighing the mass of the sample of the specified area. The deviation of the mass per unit area directly affects its mechanical properties and cost composition, and is the primary parameter for measuring the product consistency.

Tensile breaking strength and elongation at break: This indicator directly reflects the ability of the mesh fabric to resist the tensile damage and the deformation characteristics, and is the key to determining its role in bearing the stress and preventing the cracking in the rendering coat. During the testing, the warp and weft directions need to be distinguished, an electronic universal testing machine is used to stretch the specimens of the standard dimensions, the maximum breaking force and the corresponding elongation are recorded, to evaluate its load-bearing and deformation performance under the force state.

Retention rate of the breaking strength after alkali resistance: This is the core indicator for evaluating the core function of the alkali-resistant mesh fabric, i.e., the alkali corrosion resistance. After the specimen is immersed in the sodium hydroxide solution of the specific concentration for the specified time (such as 28 days), its residual tensile breaking strength is tested, and the retention rate is calculated by comparison with the original strength. This indicator directly determines the long-term service stability of the mesh fabric in the alkaline cement-based environment.

Zirconium oxide/titanium oxide content: The alkali resistance mainly originates from the alkali-resistant coating on the surface of the glass fibres or contained in the fibres themselves (often the zirconium and titanium compounds). Through the chemical analysis methods such as the X-ray fluorescence spectroscopy (XRF), the contents of the zirconium and titanium elements are quantitatively determined, which can indirectly and scientifically evaluate the theoretical basis of its alkali resistance, and is the important basis for the material qualitative analysis.

Mesh centre distance and structure: Measures the centre distance between the warp and weft yarns of the mesh fabric (such as 4 mm × 4 mm or 5 mm × 5 mm), and observes whether the mesh structure is uniform and free of the defects such as the broken warp and weft. The mesh size affects the bonding force with the mortar and the construction operability, and the structural uniformity is the premise for ensuring the uniform stress transfer. A projector or reading microscope is usually used for the measurement.

Combustible matter content: Refers to the mass percentage of the organic combustible components such as the sizing agents on the surface of the mesh fabric. It is calculated by igniting the specimen at a high temperature (usually about 625 ℃) and weighing the mass difference before and after the ignition. The appropriate binder content can ensure the bundling property and process performance of the fibres, but the excessively high content may affect the bonding compatibility with the inorganic mortar.

Testing Scope and Sample Requirements

Alkali-resistant mesh fabric for the external wall external insulation systems: This is the most important application and testing field, emphatically focusing on its ability to resist the temperature stress, structural deformation and long-term erosion of the alkaline environment in the rendering coat. The testing needs to simulate the actual working conditions, especially emphasizing the alkali resistance retention rate, tensile strength and the composite impact resistance with the rendering mortar.

Products of the different types and grammages: The testing needs to cover the various alkali-resistant mesh fabric products with the different masses per unit area (such as ≥130 g/m² and ≥160 g/m²), different mesh sizes and different weaving processes (such as the warp knitting and weft knitting). The performance emphasis and judgement indicators of the products of the different specifications may be different, and need to be carried out in accordance with the corresponding product standards.

Raw material and semi-finished product testing: The testing scope can extend to the production links, including the quality control of the raw materials such as the glass fibre strands, sizing agents and alkali-resistant coatings, as well as the preliminary performance evaluation of the semi-finished products after weaving, ensuring the stable production process and the qualified final products.

Incoming acceptance inspection and quality supervision spot checks: In the construction projects, the sampling inspection of the incoming alkali-resistant mesh fabric is an important link for ensuring that the materials meet the design requirements and contract agreements and preventing the inferior products from entering the construction site. The supervision spot checks are executed by the quality and technical supervision departments, to maintain the market order.

Research and development comparison testing: In the new product development, process improvement or the performance comparison of the products of the different manufacturers, the systematic testing and analysis is crucial. Through the comprehensive testing data, the performance advantages and disadvantages of the products are evaluated, providing the objective basis for the technical upgrading and type selection.

Durability and aging performance evaluation: In addition to the conventional testing, the accelerated aging tests (such as the alkali solution immersion, damp-heat cycling and freeze-thaw cycling) are also needed to evaluate the long-term durability, predicting its service life and performance attenuation law under the complex climate environments.

Main Testing Methods and Standard Basis

National standard GB/T methods: Mainly following the "GB/T 9914.3 Test method for reinforcement products — Part 3: Determination of mass per unit area", "GB/T 7689.5 Reinforcement materials — Woven fabrics — Test method — Part 5: Determination of glass fibre tensile breaking force and breaking elongation" and the building materials industry standard "JC/T 841-2007 Alkali-resistant glass fibre mesh fabric". These standards specify the specific technical requirements and unified test methods.

Alkali solution immersion method (core testing of the alkali resistance): In accordance with the standards such as JC/T 841, the mixed alkali solution of (5% NaOH + saturated Ca(OH)₂) or the 5% NaOH solution is usually adopted, and the immersion is carried out for 28 days (or the other agreed time) at (23±2) ℃. After the immersion, the specimen is taken out, washed with water, dried, and then the tensile strength testing is carried out, calculating the alkali resistance strength retention rate.

Direct tensile method (mechanical properties): An electronic universal testing machine is used. With the specimen dimensions (such as the strip specimens) and clamping distance specified by the standards, the tensile force is applied to the specimen at a constant tensile speed (such as 100 mm/min) until it breaks. The testing machine automatically records the force-displacement curve, and calculates the breaking strength and elongation at break.

Chemical analysis method (component determination): The instrumental analysis means such as the X-ray fluorescence spectroscopy (XRF) or inductively coupled plasma optical emission spectrometry (ICP-OES) are adopted to carry out the qualitative and quantitative analysis of the characteristic elements such as the zirconium oxide (ZrO₂) and titanium oxide (TiO₂) in the sample, verifying the alkali-resistant component content.

Ignition method (combustible matter content): The specimen is placed in a muffle furnace preheated to (625±20) ℃ for ignition for a certain time, taken out, cooled to the room temperature in a desiccator, and weighed. The mass percentage of the combustible matter content is calculated through the mass difference before and after the ignition. This method needs to strictly control the temperature and time.

Appearance and dimension measurement method: Steel rulers and tape measures are used to measure the length and width of the whole roll; a reading microscope or projector is used to precisely measure the mesh centre distance; and under a standard light source, the appearance defects such as the broken warp, broken weft, desoldering, stains and damage are checked visually or with the tools.

Testing Standards

Domestic Standards:

1. JC/T 841-2007, Alkali-resistant glass fibre mesh fabric

2. GB/T 9914.3, Test method for reinforcement products — Part 3: Determination of mass per unit area

3. GB/T 7689.5, Reinforcement materials — Woven fabrics — Test method — Part 5: Determination of glass fibre tensile breaking force and breaking elongation

International Standards:

1. ISO 4606, Textile glass — Woven fabrics — Determination of tensile breaking force and breaking elongation by the strip method

2. ISO 3374, Reinforcement products — Mats and fabrics — Determination of mass per unit area

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Electronic universal material testing machine: This is the core equipment for testing the tensile breaking strength, elongation at break and the strength after the alkali resistance of the mesh fabric. It needs to be equipped with the dedicated fabric fixtures, and the software can precisely control the tensile speed, automatically collect and process the data, outputting the maximum force value, displacement and stress-strain curve.

Constant temperature and humidity alkali solution immersion device: Used for the alkali resistance testing, including a water bath or environmental chamber that can maintain the constant temperature (such as 23 ℃), as well as the chemically stable containers (such as the plastic tanks). A pH meter needs to be equipped to regularly monitor the stability of the alkali solution concentration, ensuring that the test conditions meet the standard requirements.

Precision electronic balance: Used for determining the mass per unit area and combustible matter content, requiring the high precision (at least 0.001 g). When determining the mass per unit area, a standard sample cutter needs to be used to obtain the specimen of the specified area, ensuring the accurate weighing.

High-temperature muffle furnace: Used for the combustible matter content determination. The furnace temperature needs to be stably controlled within the range of 625 ℃ ± 20 ℃, and equipped with the high-temperature resistant crucibles and desiccator, for the ignition and cooling of the specimens.

Reading microscope or projector: Used to precisely measure the fine dimensions such as the mesh centre distance and warp and weft yarn widths of the mesh fabric. The equipment needs to have the scale or digital display functions, with the appropriate magnification, and can clearly observe the mesh structure.

X-ray fluorescence spectrometer (XRF): Used to rapidly and non-destructively detect the composition and contents of the elements such as the zirconium (Zr) and titanium (Ti) in the mesh fabric or its coating. It is an important instrument for the material qualitative analysis and the preliminary judgement of the alkali resistance, and needs to be regularly calibrated with the standard samples.