Concrete is the mixture of the following ingredients,
- Fine aggregate
- Coarse aggregate &
Concrete cloth (CC) is a unique proprietary material. It has a very wide range of applications throughout the building & civil engineering industry. Concrete cloth is a flexible; cement impregnated fabric that hardens when hydrated to form a thin, durable, water & fire proof concrete layer. CC allows concrete construction without the need for plant or mixing equipment. Simply position the canvas & just add water. CC has a design life of above 10 years and is significantly quicker and less expensive to install compared to conventional concrete.
Figure 1: Concrete Cloth Section
CC consists of a 3- dimensio- nal fiber matrix containing a specially formulated dry Concrete mix. A PVC backing on one surface of the cloth ensures the material is completely waterproof, while hydrophilic fibers (Polyethylene and Polypropylene yarns) on the opposite surface aid hydration by drawing water into the mixture. The material can be hydrated either by spraying or by being fully immersed in water. It can be easily nailed, stapled through or coated with an adhesive for easy attachment to other surfaces. Once set, the fibers reinforce the concrete, preventing crack propagation & providing a safe plastic failure mode. CC is available in 3-thicknesses; CC5, CC8 & CC13, which are 5, 8 & 13 mm thick respectively & it is as shown in Fig.1.
Concrete Cloth is a flexible, cement impregnated fabric that hardens on hydration to form a thin, durable, waterproof and fire resistant layer.
History of Concrete Cloth
The British Army just placed a sizeable order for an innovative new material that combines the flexibility of fabric with the structural performance of concrete. Unlike anything else on the market, this revolutionary technology enables the use of concrete in a completely new way. The product, called Concrete Cloth, was developed by a British engineering company called Concrete Canvas. It will soon be used to enhance frontline defenses in Afghanistan.
The story behind its inception is somewhat unusual. Four years ago, we entered a competition run by the British Cement Association. At the time, we had no idea that our entry for a rapidly deployable emergency shelter would result in the launch of our own technology development company. Our research has now included trips to disaster zones around the world, including Uganda and New Orleans.
Figure 2: CC used to sandbag protection in defenses
Four years later, the concept has matured into a technology that has applications far beyond emergency shelter. Following development funded through a combination of private equity investment and grants, the company relocated to a dedicated production site in South Wales, UK, where we have begun volume production of Concrete Cloth and Concrete Canvas Shelters.
The British Army quickly saw potential uses for this new material and started trials using Concrete Cloth as a method of reinforcing sandbag defenses. This solution, shown in Fig 2, reduces degradation of sandbag walls in harsh environments such as Afghanistan, where the combination of wind, sand, and extreme temperatures mean frequent repairs to frontline defenses. In addition, damage is caused by incoming fire and outgoing muzzle flash. Concrete Cloth is completely fireproof and has performed very well during range trials where it was tested with small-and transported medium-caliber weapons. The material comes in 10 m (33 ft) rolls to eliminate the need for heavy lifting equipment and plant machinery. This is a big advantage when operating in remote areas where most supplies have to be by helicopter. The material is then simply unrolled over the sandbag wall, secured using battens, and sprayed with water. A durable and hard wearing surface is produced within 24 hours. Key to the success of the material is the fibers that form a reinforcing matrix within the Concrete Cloth. These provide a stable failure mode, absorb energy, and help maintain the structural integrity of the concrete when impacted. A ballistic projectile will pass through the cloth, but crack propagation is limited. The sand in the sandbag is therefore retained within the concrete shell. In contrast, standard sandbag cloth will typically tear, and the fill is lost very quickly.
In January 2008, a small quantity was used on the frontline in Afghanistan to validate its performance in the field. As a result of these trials, the UK Ministry of Defense has just awarded Concrete Canvas a contract to supply 5500 m2 (6600 yd2) to the frontline.
The original concept for Concrete Canvas was to create rapidly deployable hardened shelters that required only water and air for construction. The key was the use of inflation to create a surface that was optimized for compressive loading. This allowed thin-walled concrete structures that are both robust and lightweight. The shelter, such as the one shown in Fig 3, is deployed in the following four stages:
Figure 3: CC Shelter
Delivery-the shelter is supplied folded and sealed in a sack. The 16 m2 (19 yd2) variant is light enough to transport in a pickup truck or light aircraft;
Inflation-once delivered, an electric fan is activated to inflate the inner PVC liner and lift the structure until it is self-supporting. The shelter is then pegged down with ground anchors around the base;
Hydration-the shelter is sprayed with water. Hydration is aided by the fiber matrix, which wicks water into the mixture; and
Setting-the Concrete Cloth cures in the 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 structures are designed as part of a modular system. Units can be easily linked together, allowing the space to be tailored to the application. If required, they can be demolished using basic tools. The thin-walled structure has a very low mass, leaving little material for disposal.
The University of Bath in Bath, UK, has conducted finite element analysis of the shelters, showing that the structures can withstand a high distributed compressive load. This allows sandbags, earth, or snow to be piled on top-giving the shelters excellent thermal properties and protection against shrapnel, blasts, and small arms fire.
|Figure 4: CC Bulk Rolls||Figure 5: CC Batched Rolls|
Concrete Canvas Shelters are specified to withstand 0.75 m (2.5 ft) of wet sand on the sides (sufficient to stop 7.62 mm [.30 calibers] rounds) and 0.5 m on the roof (to protect against shell fragments).
Concrete Canvas (CC) is a flexible; cement impregnated fabric that hardens when hydrated to form a thin, durable, water and fire proof concrete layer. The following data provides useful information for installers, customers and specifies of CC. It provides an overview of useful data and techniques that can be used across a wide range of applications.
There are 3 CC types available with the following indicative specifications:
Bulk Rolls / Batched Rolls
CC is available in two standard roll sizes; bulk rolls or smaller batched rolls. The quantity per roll differs between the CC types. Bulk rolls weigh 1.6T and are supplied on 6 inch cardboard tubes which can be hung from a spreader beam and unrolled using suitable plant equipment (see below). Bulk rolls provide the fastest method of laying CC and have the additional advantage of reducing the number of joints required. Batched rolls are supplied on 3 inch cardboard cores with carry handles designed as a 2 to 4 man lift. All CC thicknesses can be supplied batched to custom lengths for a small additional charge.
Examples of CC Applications
Some examples of applications for the different CC types are given in Table 2.
CC Material Properties
Compressive testing based on ASTM C473 – 07
- 10 day compressive failure stress (MPa) 40
- 10 day compressive Young’s modulus (MPa) 1500
Bending tests based on BS EN 12467:2004
- 10 day bending failure stress (MPa) 3.4
- 10 day bending Young’s modulus (MPa) 180
Abrasion Resistance (ASTM C1353-8)
- CC lost 60% less weight than marble over 1000 cycles.
Abrasion Resistance (DIN 52108)
- Similar to twice that of OPC Max 0.10 gm/cm2
CBR Puncture Resistance EN ISO 12236: 2007 (CC8 & CC13 only)
- Min. Push-through force 2.69kN
- Max. Deflection at Peak 38mm
Resistance to Imposed Loads on Vehicle Traffic Areas
EN 1991-1-1:2002 (CC8 & CC13 only)
- Category G compliant
- Gross weight of 2 axle vehicle 30 to 160kN
- Uniformly distributed load not exceeding 5kN/sq m
Initial Set≥ 120 min
Final Set.≤ 240 min.
Method of Hydration
CC can be hydrated using saline or non saline water. The minimum ratio of water to CC is 1:2 by weight. CC cannot be over hydrated so an excess is recommended. The recommended methods are: In a hot/arid environment, re-wet the material 2 - 4 hours after the initial hydration.
Figure 6: Spray The Fiber Surface With Water Until It Feels Wet To Touch For Several Minutes After Spraying.
Immersion: Immerse CC in water for a minimum of 90 seconds.
Spraying: Spray the dry CC with water until it is saturated. Do not use a direct jet of pressurized water as this may wash a channel in the material and create a weakened area
Re-spray the CC again after 1 hour if:
- Installing CC5
- Installing CC on a steep or vertical surface
- Installing in warm climates
A ‘snap off’ type disposable blade is the most suitable tool for cutting CC before it is hydrated or set. When cutting dry CC, a 20mm allowance should be left from the cut edge due to lost fill. This can be avoided by wetting the CC prior to cutting.CC can also be cut using handheld self sharpening powered disc cutters.
Cutting Set CC
Set CC can be cut as with conventional concrete, with angle grinders, construction disc cutters or good quality tile cutters.
CC Mechanical Fixing
There are a large number of mechanical fixings that are suitable for use with Concrete Canvas. Some of these fixings can be used in conjunction with the non-mechanical joining methods described later in this to improve the mechanical strength or water proofing properties of joints.
The versatility of CC means that a wide range of manual, electric or gas powered staplers are suitable for attaching CC to soft substrates such as wooden boarding for building cladding. Commercially available hand staplers are suitable for fixing 2 layers of CC together where a small amount of compression force is required.
|Figure 7: Snap off Blade||Figure 8: 3.5 Disc cutter|
|Figure 9: 3.6 Angle Girder||Figure 10: Electric Stapler|
|Figure 11: Standard Nail Attached to CC||Figure 12: Self Tapping Screw|
Standard nails can be used to attach CC. Alternatively, a power tool such as the Hilti nail gun, provides a quick and effective method of securing CC to hard surfaces such as concrete or rock. This may be appropriate where CC is being used to recondition an existing concrete surface or for spall lining in mining applications. It is important to ensure that the nail is used with at least a 15mm washer to ensure the head does not penetrate through the surface of the Canvas.
Self tapping screws provide a quick and readily available means of attaching CC to a substrate or to itself. Typical applications include sandbag reinforcement or covering existing wooden or steel structures.
Alternatively large thread ‘self drive’ screws provide an excellent method of securing overlapped layers of CC together. This is ideal where a good mechanical joint is required, for applications such as slope stabilization, dust suppression or vehicle track way.
Hog-rings are available in a wide range of sizes and can be applied to Concrete Canvas using pneumatic, electrical or hand powered tools. They provide a rapid means of securing CC either to itself or onto a wire mesh substrate such as gabion baskets. Hog-rings can also be used to attach adjacent sheets of CC together by laying the material face to face (fiber side together) and then hog-ringing at intervals along the edge. The spacing will vary depending on the level of mechanical fixing required.
If a more water proof seal is required, a Bitumen tape can be applied over the hog-rings, onto the PVC backing, using a blow-torch. Using this method, large panels of Concrete Canvas can be prefabricated with relative ease.
Figure 13: Hog Ring Used to Attach CC
Figure 14: Bitumen tape over the hog-rings Photo 3.12 Medium gauge wire
Medium gauge wire can be used as a simple alternative to hog-rings where plant equipment is not available. The end of the wire should be cut to a sharp point to aid penetration through the CC layers.
Pegging is recommended for ground surfacing applications such as ditch lining, slope stabilization or erosion control. Typically pegs are specified every 2m for most applications, but this will vary depending on the ground conditions and application. Pegs should be used at joints where possible to secure adjacent layers together. Pegs are available directly from Concrete Canvas Ltd. in a range of sizes which are suitable for use with CC. The peg must have a sufficiently sharp point to penetrate the surface of the Canvas.
|Figure 15: Peg Used to Join CC||Figure 16: Recommended Minimum Coverage|
CC Non- Mechanical Fixing
Simple CC Overlap & Simple CC Overlap (Screwed)Overlapping Concrete Canvas is the simplest method of joining 2 layers together. This is appropriate for the majority of ditch lining, erosion control and ground surfacing applications. Overlapped joints should be compressed along the entire length while the material sets to ensure there are no voids between layers. This can be done using screws, sandbags, water weights, loose fill, staples etc. Overlapping CC will provide a moderate level of water proofing and is suitable for drainage applications. We recommend overlapping cut edges by a minimum of 100mm and sealed edges by a minimum of 50mm.
CC Bonding Sealant
Concrete Canvas can be joined and sealed by applying a bonding sealant between overlapping layers. Concrete Canvas Ltd. can provide a recommended sealant which bonds to both the PVC backing and fiber surface of Concrete Canvas. A minimum bead size of 6mm should be applied along the length of the joint and the two layers firmly pushed together. The sealant works in both wet and dry conditions so can be applied before hydration or immediately after. The bonding sealant will fully cure in 24 hours.
|Figure 17: CC8 over lapped joint with CC Grout||Figure 18: Ditch lining|
|Figure 19: Slope Protection||Figure 20: Pipeline Protection|
|Figure 21: Ground Resurfacing||Figure 22: Mining Applications|
CC Jointing Grout
Concrete Canvas can be joined and sealed by overlapping layers and applying a grouting compound along the joint. Concrete Canvas Ltd. can provide a bespoke cementious grout called CC Jointing Grout for use in drainage and ditch lining applications. CC Jointing Grout is based on the same cementitious mix as Concrete Canvas to create a homogenous joint. The use of other grouting compounds may retard setting time and reduce set strength. Grout should be applied after hydrating the two overlapped layers. Ensure that the bottom layer, including the overlapped area is properly hydrated. CC Jointing Grout has similar setting characteristics to CC and initial set takes place after two hours. After applying the grout, continue to hydrate as per CC hydration instructions, ensuring not to apply jets of water directly onto the joint to avoid washout of the grout.
The fiber surface of CC can be easily painted once set using standard exterior masonry paint. This provides a quick and simple method of improving the aesthetic appearance of CC. Alternatively, Concrete Canvas Ltd. can recommend a range of copolymer concrete surface treatments which can provide a coloured uniform finish as well as hydrophobic protection against staining and organic growth. Fire retardant paints have also been shown to be effective where thermal performance is critical.
A white cement blend of Concrete Canvas is available on request subject to minimum volumes. This blend provides a brilliant white uniform finish and is most commonly used for architectural applications.
CC can be rapidly unrolled to form ditch or tank lining. It is significantly quicker and less expensive to install than conventional concrete ditch lining and requires no specialist plant equipment. The 30m ditch shown below was lined in 45min.
CC can be used as slope stabilization and other erosion control applications such as temporary and permanent slope protection, retaining walls, boulder fences, low level bunds and river bank and dam revetments.
CC can be used as a coating for overland or underwater pipeline protection, providing a superior tough rock shield. In remote areas it can be used to coat steel pipe on site without expensive wet concrete application plants. CC will set underwater and provide negative buoyancy.
CC can be secured with ground anchors to rapidly create a concrete surface for flooring, pedestrian walk-ways or dust suppression. CC8 and CC13 have been tested to EN 1991-1-1:2002 (Resistance to Imposed Loads on Vehicle Traffic Areas)
CC can be used as an alternative to poured or sprayed concrete or as a quick way of erecting strong permanent or temporary blast and vent structures and spall lining. CC has been successfully tried in Mpumalanga, South Africa.
|Figure 23: Bund Lining||Figure 24: Sandbag Reinforcement|
|Figure 25: Gabion Reinforcement / Capping||Figure 26: Dust Suppression|
Earth containment bunds can be quickly lined with CC to provide an efficient, chemically resistant alternative to concrete walling.
CC has been proven to prevent the degradation of sandbags from sustained incoming fire, outgoing muzzle fly ash and environmental exposure. A sandbag wall protected by CC withstood 900 rounds of 7.62 NATO, fired by a GPMG LR at a range of 100m. There is currently over 5500sqm of CC being used by the British Army in Afghanistan.
Gabion Reinforcement / Capping
CC can be used to cap or repair gabion walls to provide long-term protection and prevent FOD (Foreign Object Damage). Covering gabions with CC also prevents water ingress which can cause slump, whilst protecting the geo-textile membrane from the effects of UV degradation.
Dust SuppressionCC5 was developed as a result of in-theatre feedback, for use as a dust suppression surface around Helicopter Landing Sites. Benefits include: speed of installation, durability, and good coverage (CC) will conform to the underlying ground conditions).
Advantages of CC
- Rapid-the material can be hydrated by either spraying it or fully immersing it in water. Once hydrated, it remains workable for 2 hours and hardens to 80% of its final strength within 24 hours. These times can be reduced by adding accelerants into the dry mixture at the point of manufacture;
- Easy to use-dry Concrete Cloth can be cut or tailored using simple hand tools such as utility knives. The PVC side can be supplied with an adhesive backing and the fibrous side bonds well to concrete or brick surfaces when set. It can be easily repaired or upgraded using existing cement products;
- Flexible-Concrete Cloth can be easily nailed through before setting. It has good drape characteristics, allowing it to take the shape of complex surfaces including those with double curvature;
- Strong-the fiber reinforcement acts to prevent cracking, absorbs energy from impacts, and provides a stable failure mode;
- Fireproof-Concrete Cloth is a ceramic-based material and will not burn;
- Waterproof-the PVC backing on one surface ensures that Concrete Cloth is completely waterproof;
- Adaptable-Concrete Cloth is currently supplied on 1.2 m (4 ft) wide rolls but can be manufactured with a roll width of up to 5 m (16.4 ft). The cloth can be produced in a range of thicknesses from 5 to 20 mm (0.2 to 0.8 in.); and
- Durable-Concrete Cloth is chemically resistant and will not degrade in ultraviolet light.
- Environmentally Friendly
Limitations of CC
- CC cannot be over hydrated and an excess of water is always recommended.
- Do not jet high pressure water directly onto the CC as this may wash a channel in the material..
- CC has a working time of 1-2 hours after hydration. So do not move CC once it has begun to set.
- Working time will be reduced in hot climates.
- If CC is not fully saturated, the set may be delayed and strength reduced.
Engineers Incorporated Ltd (EIL) was commissioned by Concrete Canvas Ltd (CCL) to prepare a comparison of costs for lining an open, trapezoidal ditch 900 x 900 x 900mm, 500m in length.
The comparison for construction costs requested, were:-
- In Situ concrete lining, average thickness 150mm.
- Precast Concrete Paving Slabs, laid on sand / cement screed.
- Sprayed Concrete (Gunite) average thickness 100mm with mesh.
- Concrete Canvas CC8.
The above rates assume that the initial ditch excavation to form the trapezoidal shape is complete prior to commencement of lining and therefore has been excluded in the costs.
The above rates assume that the site has tarmac access for pouring in-situ concrete, delivery of sprayed concrete and paving slabs.
Analysis of Rates
- The Journal For Science, Engineering And Technology In Wales, issue 62, winter 2009