HISTORY OF CONCRETE CLOTH
The British Engineering Company had found the revolutionary material, concrete cloth. It’s a recent innovation in the concrete sector.The technology was first found for emergency shelters, application to military world and later on applied to commercial construction work.
2.1 CONCRETE CLOTH AS REINFORCING SANDBAGS
The British Army used the method of reinforcing sand bag for defence; this reduces the degradation of sandbags (figure given below) in extreme climates of Afghanistan, where the combination of wind, sand and extreme temperature affects the sandbags for a frequent repair. Moreover it was fireproof.
They are made compact to work even in remote areas by manufacturing them in a compact size (10 m or 33 ft), made them easy to handle without any of the heavy lifting equipment’s or planting machinery’s. That forms a biggest advantage when work in remote area where the helicopter is the only way to mode of transport.
The fibers used in them forms a reinforcing matrix within the concrete cloth. Thus when impacted this property of fibers used helps to serve the structural integrity of concrete. A ballistic attack may pass through them, but crack propagation is limited, as a result, the sandbags remain safe inside the concrete shell.
In January 2008, a notable amount of concrete cloths are laid in the frontline in Afghanistan to analyze the field usage and the performance which is satisfactory for the U.K army.
Fig.2.1.1 CC as reinforcing sandbags
2.2 CONCRETE CLOTH AS DEPLOYABLE SHELTER
The research of concrete clothes is to develop rapid hardening shelters only using the water and air. Concrete Canvas Shelters have two major advantages over conventional tented shelter:
1. Operational: It enables a hardened structure from day one of an operation. They provide much better environmental protection, increased security and vastly improved medical capability.
2. Financial: They have a design life of over 10 years, whereas tents wear out rapidly and must then be replaced. They are a one stop solution, saving effort and cost over the lifetime of medium to long term operations.
The key was the use of inflation to create a surface that was optimized for compressive loading. This allowed thin-walled concrete structures to be formed that are both robust and lightweight.
The University ofBath in Bath, UK, has conducted finite element analysis of the shelters, showing that the structures can withstand a high distributed compressive load.
Concrete Canvas Shelters (CCS) are supplied in polyethylene, airtight, water proof, rot proof sacks within ISPM15 heat treated timber/ply panel crates.
CCS are rapidly deployable structures that can be deployed by two people in less than 24 hours. There are two shelter sizes available, the CCS25 and the CCS50 with respective deployed areas of 25 and 50sqm.A CCS50 will require a vehicle or winch to aid with the unfolding of the shelter prior to inflation. Each shelter is provided with the ground pegs required for inflation. CCS are prefabricated structures consisting of Concrete Canvas fixed to an inflatable inner with integral steel door sets at each end. The shelter is deployed in the following four stages:
2.2.1 a. Delivery
The shelter is supplied folded and sealed in a sack. The 16 m2 variant is light enough to transport in a pickup truck or light aircraft.
2.2.1 b. Inflation
Once delivered, an electric fan is activated to inflate the inner PVC liner and lift the structure until it is self-supporting.
2.2.1 c. Hydration
The shelter is sprayed with water. Hydration is aided by the fiber matrix, which wicks water into the mixture
2.2.1 d. Setting
The Concrete Cloth cures inthe shape of the inflated inner PVC liner. The structure is ready to use 24 hours later.
Access holes allow the installation of services such as water, power, air conditioning, and heating units. The shelters have excellent thermal properties and protection against blasts, and small arms fire. A shelter using CC is shown in figure.
Fig. 2.2.1 CC as deployable shelter
Very high early strength is a fundamental characteristic of concrete cloth. The first crack strength of CC is attributed to two aspects: matrix strength and fiber bridging effect. The first crack strength σfc is defined as the applied tensile stress at which a matrix crack spreads throughout the cross section of the sample under tension. The maximum bridging stress σB is defined as the maximum stress that bridging fibers can transfer across the crack of specimen.
Typical strengths and physical characteristics are as follows:
The test is based on ASTM C473-07.By the test the 7 day minimum compressive strength is equal to 38 MPa
This tests based on ASTM C-1185. The test is used to determine the ability of material to resist the bending. The 7 day minimum bending stress is equal to 3.3 MPa and 7 day modulus minimum is equal to 180 MPa.
ASTM C1353-8 is the standard test method to determine abrasion resistance of the material. CC lost 60% less weight than marble over 1000 cycles.
Resistance to imposed loads on vehicle traffic areas:
EN 1991-1-1:2002 is the standard testing method (for CC8&CC13 only). The gross weight of two axle vehicle should be between 30 to 160 kN and the uniformly distributed load should not exceed 5kN/sq.m
CBR puncture resistance:
Test is based on EN ISO 12236:2007. The test is used for CC8& CC13. The minimum push-through force is equal to 2.69 kN and the maximum deflection at peak is 38 mm.
3.2 PHYSICAL PROPERTIES
The time between the end of mixing and initial set of a material made with a hydraulic binder or the hydraulic binder itself. The initial setting time should be greater than or equal to 120 minutes and the final setting time is greater than or equal to 240 minutes. Concrete canvas will achieve 70-80% strength in 24 hours after hydration.
The dry density of Concrete Cloth before hydration is 1500 kg/cc Upon Complete hydration the density increases 30-35% to a range of about 1950-2025 kg/cc.
Concrete Canvas is available in 3-thicknesses; CC5, CC8 & CC13, which are 5, 8 & 13 mm thick respectively. There is theoretically no limit to the thickness of the fabric, although it will generally be limited by the manufacturing techniques used to produce it. A typical thickness would be between 2 and 15mm. One important consideration limiting the thickness of the material is the ability of the liquid to penetrate through the interior of the settable material before the outer portions of the settable material is set. A further limitation on the thickness comes from the increased Weight of the fabric with increased thickness and if it is too thick, the faces may not be able to support the Weight of the settable material within the fabric.