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Guidelines for Concrete Components
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Conservation Actions
Cleaning Concrete Components | Repairing Concrete Components
General Approach
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Not Recommended
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| Determine the cause of the distress, damage, or deterioration of the concrete component requiring repair through investigation, analysis, monitoring, and testing as required. |
Initiating a repair without understanding the cause of the problem being treated.
Carrying out a repair that does not address the cause of the problem. |
| Prevent water from collecting on or around concrete components by ensuring adequate drainage off of, and away from, the concrete and the Cenotaph/ Monument as a whole. |
Applying membranes or coatings to act as 'waterproofing' for concrete features as the coatings can inadvertently trap water leading to deterioration of the concrete.
Applying either penetrating or film-forming sealers to minimize moisture absorption, as these sealers are often not removable, and both types typically change the appearance of the surface of the concrete by making it more reflective. |
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Conservation Actions
Cleaning Concrete Components
| Recommended
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Not Recommended
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| Clean using the gentlest methods possible and only when necessary to halt deterioration or remove heavy soiling or graffiti.
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| Clean concrete components using low-pressure (less than 350 kPa [50 psi]) soaking with water followed by gentle scrubbing with natural bristle brushes.
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Cleaning concrete components with water when there is any possibility of freezing temperatures.
Using detergents or household cleaners with Sodium Hydroxide (NaOH) to remove stains on the concrete, as they may adversely react with other materials or be hazardous to animals and plant life.
Blasting concrete components with abrasives, as this can damage the concrete by eroding its surface, and can damage soft or delicate materials such as wood, lead, sandstone, or marble, adjacent to the concrete of the Cenotaph/Monument.
Using biocides to kill off plants such as lichens, as chemicals in the biocide may adversely react with other materials on the Cenotaph/Monument, or be hazardous to non-target animals and plant life.
Using flame cleaning to burn off plants such as lichens, as the excessive heat may damage other materials on the Cenotaph/ Monument, such as wood, lead, synthetic caulks.
Applying coatings or paint over the concrete to present a "clean appearance" as these coatings can inadvertently trap water, leading to premature failure of the coating and the accelerated deterioration of the concrete.
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| When cleaning using low-pressure soaking and brushes is not sufficient, soaking with low pressure water (less than 350 kPa [50 psi]) followed by spraying with moderate-pressure water jets (maximum 2700 kPa [400 psi]) is generally safe for use on good quality concrete only. |
Pressure washing poor quality or low strength concrete.
Pressure washing concrete with an exposed aggregate finish.
Pressure washing concrete where soft or delicate materials, such as wood, lead, sandstone, marble, lead lettering, or carvings, form nearby parts of the Cenotaph / Monument, as the pressure of the water may damage these materials.
Adding detergents, acids, or other additives to the water when pressure washing.
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| Carry out cleaning tests to determine other appropriate cleaning approaches, if cleaning using low or moderate-pressure water and brushes does not provide a sufficient degree of cleanliness. Cleaning tests should be observed over a sufficient period of time so that both the immediate and the long-range effects of the cleaning are known, the gentlest method possible is selected, and an appropriate level of cleanliness achieved. |
Cleaning concrete surfaces with more aggressive methods, without testing or without sufficient time for the testing results to be known. |
| Protect adjacent materials during the cleaning of concrete components to avoid damage by abrasion or water infiltration. |
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Repairing Concrete Components
| Recommended
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Not Recommended
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Monitor the activity of significant cracks in the concrete before determining if repairs are necessary, including checking for:
- seasonal opening and closing of cracks;
- growth in crack length over time; and,
- the appearance of new cracks.
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Repairing cracks in concrete without first determining their causes or significance. |
Match the physical and mechanical properties of the repair concrete as closely as possible with the existing, including:
- modulus of elasticity (ASTM C469-02);
- cement to aggregate ratio;
- aggregate gradation (ASTM C136-05);
- compressive and shear strength (ASTM C39/C39M-04a); and,
- coefficient of thermal expansion.
ASTM is the acronym for the American Society for Testing and Materials. ASTM publishes standards for testing procedures and material and construction quality that are referenced by Building Codes in Canada including the National and Provincial building codes. |
Using off-the-shelf pre-packaged concrete patching compounds. |
| Where concrete is exposed and forms an important visual element of the Cenotaph / Monument, match the physical appearance of the exposed repair concrete with the existing, including: color; texture; and finish. In some cases, using aggregates from the original sources and reproducing the original construction methods, such as formwork, finishing techniques, should be considered. |
Using new coatings or finishes, not historically accurate for the Cenotaph/Monument, to cover and hide surface repairs. Re-creating architectural features after forming by sculpting with plastic concrete. Re-creating form finish details such as form lines, wood grain, or knots with grinders or trowels. |
| Create a mock-up of an exposed concrete repair as part of the repair contract to determine the suitability of the proposed repair materials and techniques in matching the physical appearance of the existing exposed concrete. It is important to prepare the mock-ups far enough in advance of the repair work to allow them to fully cure before they are evaluated (e.g. minimum 28 days), and to prepare them under the same conditions as the eventual repairs. For example, if the repair is on a vertical surface, the mock-up should be created in a vertical orientation. |
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| Clean exposed concrete to remove contaminants, dirt, and soil, before initiating repairs, so that the new concrete patches match a cleaned surface. |
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| Carry out testing of the existing concrete to determine its physical and mechanical properties, including its level of air content (percentage of voids), the presence of any impurities or contamination, and evidence of carbonation. Carry out testing far enough in advance of the repair work to allow sufficient time to identify source appropriate replacement materials. |
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| Ensure the freeze-thaw durability of the repair concrete by including an appropriate level of air entrainment as recommended by the Canadian Standard CSA A23.1 Concrete Materials and Methods of Concrete Construction. |
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| Use non-corroding reinforcement, such as stainless steel, epoxy coated steel, or glass fibre reinforced polymer [GFRP] rods, in repairs to replace or supplement existing corroded reinforcement. |
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| Match the amount of reinforcement to the existing, unless the repair is treating a case of damage resulting from overloading of the concrete. |
Over or under reinforcing the repair location. |
| Remove and replace all unsound concrete. It may be necessary to limit the size of the chipping equipment used on early concrete features to better control the degree of removal, as the compressive strength of the concrete may be much lower than modern concrete. |
Replacing entire concrete features, when selective replacement and repair is possible. |
| Remove all corrosion from existing exposed reinforcement that is to remain using wire brushes or sandblasting. |
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| Ensure proper concrete mixing, placement, and curing procedures by following the recommendations of the Canadian Standard CSA A23.1 Concrete Materials and Methods of Concrete Construction. |
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Ensure good chemical and mechanical bonds between the repair material and original concrete by:
- sandblasting the exposed concrete in the patch area;
- air-blasting the patch area to remove any dirt, debris or contaminants;
- pre-wetting the patch area before adding the patch material;
- brushing a slurry made from the repair concrete onto the exposed concrete of the patch area to act as a bonding agent;
- undercutting the edges of patches and cutting the patches square to develop a good mechanical bond;
- introducing supplemental anchors (e.g. stainless steel dowels) to tie the patch to the existing concrete;
- insuring an appropriate minimum thickness of the patch material is applied (i.e. do not feather the edges of the patch); and,
- chipping around all existing rebar a distance at least equal to the size of the largest aggregate used in the repair concrete.
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| Seal inactive cracks by pointing with a cementitous mortar or injecting epoxies to prevent the ingress of moisture into the concrete mass through the crack. |
Pointing cracks with mortar or other hard materials without first determining if the crack is active or not.
Sealing active cracks with hard mortars or other hard materials, which could prevent the seasonal movements at the crack.
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| Control the propagation of thermal expansion/contraction cracks by saw-cutting crack control joints into the concrete at strategic locations to force the concrete to crack at that specific location. |
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| Maintain a record of the date and extent of the conservation actions to guide future research and treatment. |
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Canada Remembers 
