Anti-Crack Test Results for Welded Wire Mesh & Fiberglass Mesh
Nowadays, the exterior and interior wall usually are made of the plaster mortar. The plaster mortar is of high brittleness and of low tensile strength so there are cracks on plastering. The plaster mortar would lose water and shrink when the plaster mortar is plastered on the wall. This kind of shrinkage usually happens during the plasticity stage for 1–2 hours. It happens when the surface luster disappears and ends when the mortar congeals. The tensile stress in the plaster mortar would increase when the shrinkage is influenced by the embedded parts. There would be cracks when the mortar's anti-tensile strength cannot resist the tensile stress. When the temperature is high, the air humidity is high and the air flows quickly, the water evaporates a lot and the wall would crack. It would cause accident easily when there are too many cracks. To prevent cracks we usually add the fibre to the mortar or install the mesh on the plaster mortar. By this way, we could control the cracks and reinforce the wall. We install the fiberglass mesh and galvanized welded wire mesh. The galvanized welded wire mesh is used widely because the welded wire mesh is economic and it's easy to construct. We make the anti-cracks experiment for the welded wire mesh.
Galvanized welded wire mesh as plaster is to anti-cracks.
The fiberglass mesh could increase the wall crack resistance as the plaster layer.
The experimental basis and principle.
The bottom of the model is made of five-plywood and around the model is hardwood frame. The bottom and the frame are reinforced well. There are two layers plastic film and in the plastic film is steel mesh frame of 8 mm wire diameter. There are four steel ends welded on the four angles. The height from the steel end to the model bottom is 6 mm.
The experiment principle. We use the specimens simulate the practical engineering. The steel frame is to constraint the shrinkage of the four angles and reinforce the welded wire mesh. The shrinkage would happen on the middle of the specimen. The bottom of the model should be sealed up and is impermeable. It would decrease the effect of the model shrinkage deformation. And we simulate the heavy wind and the high temperature to dry the water so that the model would shrink for a short time and test the welded wire mesh.
The raw material and the experiment process.
- The raw material: the cement, the P·O32.5R Portland cement, the medium fine sand, lime plaster, galvanized redrawing wire welded wire mesh, fiberglass mesh of mesh opening 5 mm × 5 mm. The density of the fiberglass mesh is 75±5 g/cm2. The width of the cloth is 100–120 cm, its gum content is more than 15％, the alkali resistance is more than 60％, the vertical density is 138 tex and the latitude density is 150 tex. The vertical crack strength is 900 N/mm and the latitude crack strength is 900 N/mm. The following is the specification of the galvanized welded wire mesh.
- The mix proportion.
- The experiment process.
Reinforce the welded wire mesh on the welded wire mesh frame, put the model on the neat ground, put the steel frame on the middle of the model, mix the mortar, pour the mortar to the model, open the fan and heating lamp, beam for four hours, blow for twenty four hours and measure the crack width and length.
|The force for cracks
|GW-1||0.41||6.35 × 6.35||210|
|GW-2||0.41||12.5 × 12.5||235|
|GW-3||0.64||12.5 × 12.5||390|
|GW-4||0.64||19 × 19||370|
|GW-5||1.07||12.5 × 12.5||580|
|GW-6||1.07||19 × 19||550|
|GW-7||1.07||25 × 25||575|
|GW-8||1.47||25 × 25||870|
|Note: The packing specification is 25 × 0.914 m/roll.|
|The mortar||The mix proportion||The water and cement proportion|
|the cement mortar A||cement: lime plaster: medium fine sand = 1: 1: 6||0.60|
|the cement mortar B||cement: lime plaster: medium fine sand = 1: 1: 5||0.60|
|the cement mortar C||cement: medium fine sand = 1: 1.5||0.55|
The experiment result and assessment.
- The anti-cracks assessment basis.
We divide the cracks for five classes on its width and every class is according to the weight value. The W means the cracks index and its the mortar cracks degree. The γ means the cracks resistance index and its the experiment mortar cracks resistance degree.
|The crack width d (mm)||d ≥ 3||2 ≤ d ＜ 3||1 ≤ d ＜2||0.5 ≤ d ＜1||d ＜ 0.5|
|The weight value A||3||2||1||0.5||0.25|
W = ∑(Ai × Li)
- W: the cracks degree (mm)
Ai: the weight value
Li: the cracks length (mm)
- γ = [(W₀-W₁)/W₀] × 100%
γ: the cracks resistance proportion (%)
W₀: the normal mortar cracks index (mm)
W₁: the mortar with putting anti-cracks welded wire mesh (mm)
|The number||The mortar||The anti-cracks material||cracks resistance proportion γ/%|
The experiment result analysis.
The effect for installing the welded wire mesh.
During the experiment, the crack time is almost the same for the same class mortar specimen. That means the welded wire mesh and the size of the welded wire mesh is not the main reason that cause the cracks. There are not many cracks for the early mortar shrinkage. The cracks happen when the mortar freezes for 1–1.5 hours.
- On the early shrinkage for the mortar, the galvanized welded wire doesn't affect mortar cracks. But after 1.5 hours, when the mortar begins to freeze the welded wire mesh is helpful for cracks resistance.
- For the galvanized welded wire mesh of wire diameter 0.64–1.47 mm, the cracks resistance effect is better with the 12.5 × 12.5 mm mesh opening than the 19 × 19 mm mesh opening.
- The mesh opening is 12.5 × 12.5 mm. The crack resistance would be better when the wire diameter increases (0.64–1.07 mm).
- The crack resistance effect of the appropriate welded wire mesh is alike the fiberglass mesh during the early shrinkage.
- The crack resistance is not good when the wire diameter is thin and the mesh opening is dense. It isn't suitable for the normal interior wall plastering anti-cracks.
- When the wire diameter and the mesh opening gets the limit (wire diameter: 1.47 mm, mesh opening: 25 × 25 mm), it cannot make a difference for the early cracks. This kind of welded wire mesh is suitable for the exterior plaster anti-cracks.
- The goal for plastering the welded wire mesh on the interior wall is to prevent the connecting, door, widow and embedded pipeline from the cracks. The plaster welded wire mesh specification: galvanized welded wire mesh, packed in roll, wire diameter of 0.8–1.2 mm and mesh opening from 12.5 × 12.5 mm to 19 × 19 mm.
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