Civil Crack repair of concrete paving and structures
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Civil Crack repair of concrete paving and structures
1. Defects on concrete paving can be due to the use of excessive water, poor cement, poor construction practices, improper mixture proportioning, and dirty or low quality aggregate and inadequate curing.
2. A deficiency must be differentiated from the actual cause and it is imperative that causes and not symptoms are dealt with wherever possible or practical. For example, cracking is a symptom of distress that may have a variety of causes.
3. Hollow spaces and cavities left in concrete mass on surface or inside the concrete mas where concrete could not reach. These look like honey bees nest and honeycombs which are on sides are visible to naked eyes and can be detected easily as soon shuttering is removed.
4. Due to non-reaching of concrete to all places in which cavities and hollow pockets are created. Main reasons are improper vibration during concrete, less cover of reinforcement bars and the use of a very stiff concrete.
5. Selection of the correct repair technique for cracking depends on knowing whether the racking is due to repeated thermal cycling, accidental overloading, drying shrinkage, inadequate design or construction, or some other cause. Only after the cause or causes are known can rational decisions be made concerning the selection of a proper repair system.
Work Procedure Civil Crack repair of concrete paving
1) Surface Preparation & Repair Method
a. Surface preparation shall be done in accordance with the materials manufacturer’s recommendation as indicated in this Method Statement, technical data sheet as per attachment.
b. As per manufacturer’s recommendation approved repair materials shall be applied by skilled mason assuring that this material pushed to fill all surface voids.
c. All identified surfaces shall be repaired in accordance with the following methods:
I. CRACKS less than 1.00 mm
Cause: Hot temperature and changes in moisture content
Width: 0.3 to <1 mm
Proposed Action: These cracks are barely visible, do not affect the structural integrity of the slab, and only allow an insignificant degree of water penetration. It is proposed to leave these cracks as they are.
II. CRACKS wider than 1.00 mm but less than 2.00 mm
Cause: Caused primarily by accidental overloads
Width: >1 mm to <2 mm
Proposed Action: These cracks are easily visible and may allow a small amount of water to penetrate. However, structural integrity is not compromised. These types of cracks should be sealed to protect the reinforcement.
As per SAER-5803, Concrete Repair Manual, Section 5.2.4, “Cracks wider than about 1.0 mm on the horizontal surfaces can usually be sealed by filling them with cement grout. This is commonly done by brushing in dry cement followed, if necessary, by light spraying with water.”
Ill. CRACKS wider than 2.00 mm
Cause: Caused by accidental overloads or subgrade settlement
Width: >2 mm
1) If no observable subgrade settlement:
a. As per SAER-5803, Concrete Repair Manual, Section 5.2.4, “For cracks wider than about 2 mm, it may be preferable to use a cement water grout. Alternatively, cracks can be widened to a width of 5 to 10 mm and pointed up with cement and mortar”.
However, based on previous repairs, cement water grout easily flakes and breaks because of brittleness. It is proposed to repair the cracks using the procedure in ACI 224.1 R, Causes, Evaluation, and Repair of Cracks in Concrete, Section 3.3, “Routing and Sealing” using approved joint sealant material.
2) If there is observable subgrade settlement:
a. Cut and replace the concrete slab after rectifying the subgrade.
b. Chipping with a V-Grove cut to the depth of the developed cracks to enlarge and clean the area by blowing out with oil free compressed air washes the chipped and allows drying.
c. Brushes apply of suitable repair material on the exposed steel reinforcement rods and chipped surface. Mix components of the approved repair materials shall be applied accordingly to the manufacturer’s instructions.
d. Area shall be free of contaminants such as oil, grease, dirt or fine particles of concrete which will prevent material penetration and bonding and may reduce the effectiveness of repairs.
2) Concrete Defects
a. Shrinkage Cracks – Repair of concrete after the plastic shrinkage cracks have formed usually consists of sealing them against ingress of water by brushing in cement or low viscosity polymers.
b. Settlement Crack – Remedial measures after the concrete has hardened consist of sealing the cracks in order to protect the reinforcement. However, consolidation of concrete immediately after the cracks start to form is by far the best course of action.
c. Dormant or Dead Cracks – Cracks wider than about 1.0 mm on the horizontal surfaces can usually be sealed by filling them with cement grout. This is commonly done by brushing in dry cement followed, if necessary, by light spraying with water.
d. Live Cracks – The sealant must then be adhered to the sides of the chase but debonded from the bottom so that the movement is spread over the full width of the chase.
e. Thermal Crack – These types of cracks should be sealed to protect the reinforcement by brushing in cement or low viscosity polymers.
f. The mortar should be applied over the whole area of the concrete with a rubber faced float, and finally it can be rubbed down with a smooth stone or mortar block for a smooth finish.
g. Repair Inadequate Cover
• If the face of the concrete is weak, it should be scabbed or grit-blasted to provide a sound, roughened surface. If it is sound but smooth, it will usually be cheaper to apply a coat of polymer-modified cement and sand, in proportions of about one part of cement to two parts of sand, before applying the first coat of rendering.
If it is not possible to increase the dimensions of the structure, a surface coating can be applied. Such a coating should be of a type having low permeability to carbon dioxide and moisture, but it should preferably allow water vapor to escape from within the concrete.
h.Repair of concrete surface defects
Repair & rehabilitation of deteriorating structures is essential not only to utilize them for their intended service-life but also to ensure the safety and serviceability of the associated components. -SAER 5803 para.4.1
One of the appropriate repair materials is the cementitious mortar which is included on the list of Saudi Aramco Engineering Report (SAER 5803 para.4.2.1 -Repair Mortars). Portland cement concrete can be used as patching materials as per ACI 546.1 R and ACI 303 (ACI 515.1 R, Sec.3.2.1 ). Cementitious repair mortar is applicable for the following concrete surface defects but not limited to:
1.Uneven surfaces & edges termination -refers to the unleveled edges of concrete pavement to guard posts, catch basins, clean-outs, manhole structures etc.
References & Standards
4. ACI Standard
a) ACI -224.1 R – Causes, evaluation and repair of cracks
b) ACI 546.1 R & ACI 303 – Patching with Portland Cement Concrete
c) ACI – 515.1 R, Sec.3.2.1 – Removal & repair of defects procedure
d) ACI – 515.1 R, Sec.220.127.116.11 – Patching Material
3. Saudi Aramco Standard
a) SAES – Q – 001- Criteria for design and construction of concrete structures
b) SAER – 5803 – Concrete Repair manual chapter 4 and chapter 5
Tools & Equipment Crack repair of concrete paving
1) All tools and equipment shall be inspected by HSE department in accordance with specifications and requirements.
2) All of tools and equipment e.g. hand and power tools etc. require special attention and protection for their use and guidelines.
3) All damaged, unsafe or defective tools will be marked, tagged as unsafe or with a red paint and taken away from operation to assure that no one will use such tools on the job.
4) Electrical tool and equipment shall be used in accordance with GFCI requirement.
a. Wire brush
b. Hammer & Chisel
c. Application Trowels
d. Smoothing Floats
e. Mixing Container
f. Drill and Mixing Paddle Small Quantities
g. Double Mixing Paddle Medium Quantities
h. Forced Action Pan Mixer Large Quantities