GRC Method Statement

What is GRC Method Statement?

A GRC Method Statement is a document that outlines the step-by-step procedures and guidelines for the installation, handling, and safety measures related to Glass Fiber Reinforced Cement (GRC) materials. It provides a detailed plan and description of how GRC products should be used, including their transportation, storage, installation, and maintenance.

This document is crucial in construction and architectural projects involving GRC to ensure that the work is carried out efficiently, safely, and in accordance with established standards and specifications.

1- Introduction

The term Glassfibre Reinforced Concrete (GRC) is used to describe products crafted from a mixture of hydraulic cement and fine aggregate, strengthened throughout by alkali-resistant glass fibers. The fiber content typically ranges from 3% to 5% by weight, with a cement ratio of up to 1:1, allowing for customization to meet specific application needs.

GRC encompasses a range of composite materials that combine the robust compressive strength properties of cement mortars with significantly enhanced impact, flexural, and tensile strengths, thanks to the fiber reinforcement.

GRC products are known for their safety, excellent chemical resistance, and resistance to rotting or corrosion.

GRC primarily consists of inorganic materials, which means it won’t burn, produces minimal smoke, and offers robust fire resistance.

Additionally, GRC is typically of relatively thin cross-section, resulting in a lower component weight. This feature enables savings in handling, storage, transportation, and installation when compared to traditional concrete products.

2- Raw Materials

2-1-AR Glass Fiber: Alkali-resistant glass fiber with high cement durability (with a minimum of 16% zirconia content) is employed in GRC production. Notably, the unprotected “E” glass type, designed for reinforcing plastics like “GRP,” should be avoided. This glass fiber is chopped and simultaneously sprayed with the cement matrix material, enabling the creation of composites with intricate profiles. Common fiber lengths range from 38 to 51 mm, although lengths less than 25 mm are used for special applications, such as decorative cornices, sills, and coping.

2-2-Cement: The most commonly used cement in GRC is Ordinary Portland Grey Cement (OPC). While other cement types, such as White Portland Cement, High Alumina Cement, and Rapid Setting Cements, may be utilized in specific scenarios, extra care must be taken in their handling, curing, and prevention of discoloration. It is essential that Portland Cement adheres to the ASTM C150 Specification for Portland Cement.

2-3-Sand: Incorporating sand in the slurry serves to reduce drying shrinkage and the risk of subsequent cracking. The preferred sand is washed and dried silica sand, free of contaminants and lumps, meeting the compositional requirements of ASTM C144 “Specification for Aggregate for Masonry Mortar,” which stipulates a minimum of 96% silica content.

2-4-Water: The use of potable water, free from any deleterious substances that might affect the GRC’s color, setting, or strength, is imperative.

2-5- Admixtures: For specific property enhancements in GRC, standard commercially available admixtures like water reducers, accelerators, retarders, and acrylic thermoplastic copolymer dispersions may be employed. Admixtures must adhere to the requirements outlined in ASTM C494, “Specification for Chemical Admixtures for Concrete.”

2-6- Inserts: Steel connection devices incorporated into the panels should be corrosion-resistant, with options like zinc-coated or epoxy-painted surfaces.

2-7- Joint Sealants and Fillers: High-performance sealants that meet ASTM C920 standards, such as polysulfides, urethanes, or silicones, are recommended. Additionally, a compressible polyethylene foam or polyurethane backup rod, or an equivalent, should be used.

2-8- Pigments: When pigments are necessary to color GRC, special attention is essential to achieve color uniformity and prevent fading or alteration over time.

3-Mould Design

The mold design plays a crucial role in several aspects: a) It impacts the ease and speed of filling the mold. b) It influences the ease and speed of demolding the product. c) It affects the quality of the final product. d) It determines the surface appearance of the product.

Selecting the appropriate material for a well-designed mold is essential. You can choose from:

a) Timber, suitable for short production runs.
b) GPR (Glass Fiber Reinforced Plastic), ideal for long production runs and well-shaped products.
c) Steel, a reliable choice for standard products.
d) Rubber molds, which can be used for various applications.

Each product may have unique mold requirements.

Designing Moulds

When designing molds, it’s important to follow these fundamental guidelines:

Avoid sharp corners in the mold design.
Incorporate tapering in the mold to facilitate demolding (approximately 5 degrees).
Ensure the mold’s structural strength.
Design the mold for easy disassembly, cleaning, and reassembly.
Pay close attention to joints to prevent any leakage.

4-Manufacturing

The production of Glass Fiber Reinforced Concrete (GRC) typically involves two methods: the “spray” process and the “premix” vibration casting process. The choice of method depends on various factors, including strength requirements, mold size, product shape, and the installation system. In general, “sprayed” GRC is preferred for larger, thin items (e.g., building cladding panels), while “premix” GRC is used for smaller items with greater thickness.

Sprayed GRC tends to be stronger than premix vibration cast GRC, as it can achieve a higher fiber content of 5%, while premix GRC is usually limited to around 3%.

4-1-Mix Design (Comparison between Sprayed GRC and Premix GRC):

For both Sprayed GRC and Premix GRC, the mix design includes:

50kg of sand
50kg of cement
Water: 16-17 liters for Sprayed GRC, 18-20 liters for Premix GRC
The use of plasticizer depends on the type and manufacturer’s instructions.
The addition of polymer is optional.
Glass fiber content: 3-5% by weight for Sprayed GRC, 2-3% by weight for Premix GRC
Typically, fiber lengths range from 25-50mm for Sprayed GRC and 12-25mm for Premix GRC.

4-2-Methods of Manufacturing GRC

4-2-1-Sprayed GRC:

a) In the spray-up process, water, admixture (and polymer if used) are mixed in a “high shear mixer.” Sand and cement are added slowly until a smooth, creamy slurry is achieved, with a mixing time of about 1-2 minutes.

b) Once ready, the mix is transferred to a “pump/spray unit.” The pump conveys the slurry at a regulated rate of flow to the spray gun.

c) At the spray gun, a continuous strand of glass fiber is introduced into the compressed-air-powered gun. The strand is chopped into predetermined lengths and combined with a sand and cement slurry.

d) The operator manually moves the spray head back and forth across the mold. Initially, a thin slurry or mist coat (about 1.5-2mm) is sprayed without reinforcing to provide a cover for the glass fiber on the finished surface. The stream of material is directed perpendicular to the mold surface, gradually building up the required thickness of GRC.

Roller compaction is used to ensure mold face compliance, fiber slurry impregnation, air removal, and the development of adequate density. The rolled surface can be smoothed with a trowel. Thickness control is maintained using pin gauges. A single hand unit typically yields 10-12 kg of GRC per minute. This process results in one surface with an ex-mold finish and the other with a rolled or troweled finish.

4-2-2-Premixed GRC

In all premix processes, cement, sand, water, admixtures, and chopped strands of alkali-resistant (AR) glass fiber are mixed together in a mixer before forming the GRC product.

5-Demoulding

To facilitate demolding, a release agent can be applied to coat the entire inside surface of the mold. This can be done either through spraying or by using impregnated sponges or cloths. Any excess GRC that might impede demolding should be removed. It’s worth noting that applying a steady force is more efficient and quicker than using a hammer to release the mold.

6-Curing

6-1 Initial Cure: After the panel is completed in the mold, it should be kept covered with polythene overnight for 12-24 hours. This initial cure helps prevent drying and ensures that the GRC panel attains the necessary strength for stripping.

6-2 Controlled Curing: Following the initial overnight curing, the product is removed from the form and placed in a controlled curing environment. Proper curing not only influences strength gain but also prevents issues like warping due to moisture content variations and surface appearance problems like porosity, staining, and efflorescence. Panels should be adequately supported to avoid curing marks or staining. Additionally, correct panel support during storage minimizes the risk of warping or bowing.

7-Quality Control

The quality of manually sprayed GRC relies on the operator’s skill. A comprehensive quality control program must encompass material control tests. GRC elements should bear markings indicating the date of manufacture and an identification number that corresponds to production and erection drawings and testing records.

7-1-Test Procedures:

7-1-1-Production Testing (wet):

a) The Slump Test: This test determines the slump value of the cement slurry, indicating its suitability for spraying.

b) The Bag Test: This test assesses the glass fiber roving chopping rate.

c) The Bucket Test: It determines the slurry flow rate.

d) The Wash-Out Test: This test measures the glass fiber content.

e) Panel thickness should be frequently checked at various points on the panel surface during the spray-up process.

Thickness of GRC Skin:

• Hand spray: 5mm to 8mm
• Premix: 10mm to 100mm

7-1-2-Production Testing (After Curing):

a) Flexural Testing
b) Determination of Bulk Density
c) Shear Testing

8-Tolerances

8-1 Allowable Tolerances for Manufactured width of units adjacent to the form:

• Units 300 cm. or under: ±.3mm
• Units between 300-600 cm: ± 3mm to ± 5mm
• For each additional 300mm: ±3mm

b) Thickness Tolerance: Skin thickness +3mm

8-2 Allowable Tolerances for Erected Units:

a) Overall Height and Width at the face of the joint for panel dimensions:

• 300 cm. or less: ±4.6 mm
• 300-600 cm.: ± 4.6mm to ± 6mm
• For each additional 300mm: ±3mm

b) Warpage Tolerance: One corner may be out of plane of the other by +3mm.

c) Bowing Tolerance: Not to exceed L/360, where L represents the panel length.

9-Loading and Delivery

G.R.C products are typically transported using tractors and semitrailers. However, transportation by rail or barge over longer distances is also feasible. Normal highway restrictions for weight and size must be adhered to. Due to their thin-walled construction, G.R.C panels offer significant cost savings in terms of delivery.

Panel configurations should be designed to allow nesting for maximum truck load efficiency. When nesting or stacking panels vertically, consideration should be given to the proper distribution of vertical loads to prevent progressive crushing.

Loading the panels for delivery should be the reverse of the erection sequence to enable installation directly from the trailer and reduce handling and storage costs.

To protect panel edges during shipment, suitable soft materials include high-density polymer, polystyrene, and elastomeric materials. The trailer bed’s flexibility is best supported at two points. The need for protective covering against road stains and weather should be evaluated in terms of cost and effectiveness during transportation.

Nylon straps should be used to secure the load, with special attention paid to protecting the panels at the binding points of the straps and preventing the “slap” effect of long straps. Over-tightening of straps should be avoided to prevent panel deformations.

Site conditions should allow erection equipment and transportation units to proceed under their own power to the location where G.R.C panels can be handled directly by the erection equipment.

If onsite storage is necessary, it should be on relatively level and firm, well-drained ground, with minimal risk of damage due to other construction activities.

If a loaded trailer is left at the jobsite, precautions should be taken to block the trailer to prevent accidental overturning, especially on frozen sites subject to thawing. The dropped trailer should be parked on firm, level ground, and panels should be lifted slowly from the transport vehicle. If any binding occurs, the unit should be lowered, and the obstacle holding the unit should be removed.

When unloading a stack of panels, the exterior unit should be unloaded first to prevent chipping and scraping. Panels should not be slid out from the middle of a stack. If possible, when dealing with a load containing many panels, balance should be maintained by unloading alternate sides of the vehicle or by blocking the vehicle.

10-Installation

10.Coordination

Efficient jobsite operation relies on effective planning involving the manufacturer, trucker, erector, and the general contractor. Ensuring jobsite access for all necessary The erector requires a steady panel supply for seamless progress on the jobsite. GRC Elements should be erected on flat surfaces after the final plastering to guarantee precise adjustment.

For secure fixation, anchor bolts must be positioned at least mm. away from the edges. Prior to aluminum or glass work, GRC elements should be erected.

10.2-Erection

Supervising erection demands expertise in handling and positioning panels on the building. Thorough advance planning ensures the presence of all necessary tools, equipment, and loose connection hardware. Jobsite conditions must properly accommodate the erector’s equipment operating under its own power. Advance field layout work is indispensable to maintain horizontal and vertical control during panel positioning.

Ideally, panels should move directly from truck to building to minimize hazards and costs associated with extra handling. If jobsite storage is required, the erector must adhere to proper yard storage practices. Consulting with the manufacturer about storage methods is essential if not outlined in the erection drawings. The lightweight G.R.C panels allow for lighter and more cost-effective handling equipment.

A straightforward hoist on the roof or a small crane may suffice. Caution is advised during lifting as the lightweight G.R.C panels are less wind-resistant compared to heavier concrete units. The erector should comprehend the function and performance of each connection detail to ensure panels align with the design concept.

Any field modification to the steel stud frame or connection system must receive approval from the engineer responsible for the design. If connections necessitate temporary support like shims, they should be promptly removed to ensure the connection system functions as intended.

Welding in temperatures below 20F (- 7 C) should be avoided due to the risk of fractured welds. A successful installation hinges on the erector’s grasp of product manufacturing and erection tolerances, along with allowable variations in building frame construction.

When installing panels, priority is given to aligning the exterior face for aesthetic reasons. This may lead to the interior stud face not aligning perfectly. Panel design typically prevents stud spacing, thus it’s recommended that if the studs are to receive interior drywall or similar treatment, the interior finish should be mounted on shimmed transverse channels rather than directly on the stud.

Window frames should be directly attached to the head and sill tracks of the steel stud frame (or a separate framing system). The stud frame bears the window load, both dead load and wind pressure, transferring it through the frame to the panel connections attached to the structure. The glazier shims the window frame to its proper location before screwing it onto the steel stud frame.

The only contact between the window frame and the G.R.C skin is the joint sealant, allowing the skin to move and preventing undue restraint. The G.R.C skin may expand and contract up to 1/8 in. per 10 ft. (3mm per 3 m) due to moisture and thermal effects. Ignoring this may lead to improper installation of the window frame, resulting in excessive restraint of the G.R.C skin, potentially causing issues.

G.R.C skin also ensures the wall system remains weathertight. Insulation, electrical, and telephone conduits may be placed in the wall cavity formed by the steel stud frame. Insulation and other trade items are installed on-site by other subcontractors.

10.3-Painting

Exterior surfaces should receive a breathable paint, allowing water vapor passage while blocking liquid water. Painting of GRC works should precede the application of general facade paint to prevent mesh dirt.

10.4-Cleaning

Many G.R.C panel projects may only require spot cleaning with soap and water in isolated areas, while others may necessitate a comprehensive cleaning. Stubborn dirt may call for a commercial cleaning compound or a diluted muriatic acid solution. Wetting the G.R.C surface beforehand helps prevent deep absorption by potent cleaners.

A 3 to 5 percent phosphoric acid solution may be more effective on white concrete and also aids in avoiding yellow stains. When using acids, special care must be taken to mask and protect adjacent materials to prevent damage.

10.5-Patching and repair

Due to their inherent resilience and ductility, as well as their light weight and high resistance to crack propagation, G.R.C panels should experience minimal chipping and spalling during storage, delivery, and handling.

Nonetheless, some level of repair is expected as a routine procedure. Production blemishes should have been rectified at the plant. Given that patching and repair of G.R.C is a specialized task, it’s advisable to employ manufacturer’s personnel for such work.

They possess knowledge of bonding agents and shading or texturing techniques. There may be instances where a composite patching mix reinforced with glass fiber is necessary. Damage affecting structural capacity should be discussed with the design engineer. Generally, the extent of patching and repairing should be minor.

10.6-Joint sealing

Architectural considerations and tolerance realities often dictate the use of one-stage or two-stage joints employing elastomeric sealants. In the United States, one-stage joints are more commonly used, typically involving a sealant close to the exterior surface. A minimum G.R.C panel return of ½ in. (38 mm) at the joints is recommended, with 2 in. (51mm) preferred.

Installed project joints should undergo inspection for satisfactory tolerance and cleanliness, free from dust and contaminants. If a primer is advised by the sealant manufacturer, caution should be exercised to avoid staining the panel’s outer face. The recommended backup rod of appropriate size should be set at the correct depth of the joint.

When inserting a polyethylene foam backup rod, a blunt tool should be used to prevent puncturing the rod and potential out-gassing, which could lead to sealant blistering. It’s imperative to meticulously adhere to all recommendations provided by the sealant manufacturer.

11-Standards and Specifications

11-1 British Standards Institution:

BS 6432:1984 British Standard Methods for Evaluating Characteristics of Glass Fiber Reinforced Cement Material.

11-2 Glass Reinforced Cement Association (GRCA):

GRCA S0105 Specification for Alkali Resistant Glass Fiber for Strengthening Cement and Concretes. GRCA S0110 Specification for the Production of Glass Fiber Reinforced Cement (GRC). GRCA S 0106 Guidance for Defining Specifications for Glass Fiber Reinforced Cement Cladding.

11-3 American Society for Testing and Materials (ASTM):

ASTM-C947-89 Standard Test Method for the Flexural Properties of Thin Glass Fiber Reinforced Concrete Sections.

12-Safety

Safety working conditions must be guaranteed through the oversight of a safety inspector.