Concrete resurfacing is a technique used to restore worn or damaged concrete floors or pavement surfaces, enabling them to be used without having to reconstruct the entire structure. However, before any resurfacing method can be applied, it is essential to evaluate the existing surface. This evaluation is necessary to determine whether the current layer meets specific design considerations.
The evaluation process involves a thorough inspection of the surface, which includes checking for any cracks, holes, or other forms of damage. It also involves assessing the surface’s strength, stability, and overall condition. The information gathered during the evaluation is then used to determine the best course of action for resurfacing the concrete.
The evaluation process is crucial because it helps to ensure that the resurfacing method used is appropriate for the existing surface. Using the wrong resurfacing method could lead to further damage or failure of the surface, which would ultimately result in more costly repairs.
Therefore, it is essential to conduct a comprehensive evaluation of the existing surface before undertaking any concrete resurfacing project. This will help to ensure that the resurfacing is successful and that the surface can be used effectively without the need for complete reconstruction.
Requirements of an Existing Concrete Pavement Surface
Before undergoing resurfacing, there are several crucial factors that must be considered to ensure the successful completion of the service. Firstly, the existing layer must have sufficient thickness to carry out the necessary work. If the layer is too thin, resurfacing may not be feasible.
Secondly, if there are longitudinal and transverse joints present on the concrete surface, they must be able to transfer load smoothly to the underlying layer without compromising the smoothness of the surface once the resurfacing is completed. Any cracks or joints present must also be able to prevent the penetration of fine solids or moisture.
Thirdly, in order to withstand severe exposure conditions, the reinforcement must have adequate cover and be sized and spaced to ensure tight crack control.
Fourthly, the maximum size of aggregates used in the service must be based on the thickness of the resurfaced layer and steel spacing.
Fifthly, durable aggregates must be employed, particularly in areas where freezing and thawing problems may occur. Air entrainment may also be necessary, and the use of de-icing salts can be employed.
Finally, for the construction of shoulders, concrete or other stabilized materials must be used to prevent the infiltration of shoulder materials between the underlying pavement and the resurfacing layer.
Evaluation of the Existing Concrete Floor or Pavements for Resurfacing
Before resurfacing existing pavements, it is essential to evaluate their condition. This evaluation involves three basic elements: the evaluation of functional condition, the evaluation of distress through surveys, and the evaluation through structural testing. Although these criteria are not mutually exclusive, they may occur individually or in combination, which can influence the decision regarding resurfacing.
To select the best overlay option, it is crucial to understand the true condition of the existing pavement. This understanding must provide insight into how the pavement will behave when a new overlay is laid over it. Structural evaluation is a more critical consideration than functional evaluation in determining the true condition of the existing pavement.
Therefore, the evaluation of the existing pavements is a crucial step in the resurfacing process. It helps to determine the overlay option that is most suitable for the pavement’s current condition, considering both functional and structural evaluation. Ultimately, this evaluation ensures that the new overlay will perform optimally, improving the pavement’s longevity and serviceability.
Functional Adequacy of the Old Surface
The serviceability condition of a pavement is primarily concerned with its surface and how it holds up under traffic. It is determined by evaluating the pavement’s ride quality using panel ratings. Many agencies assess the condition of the pavement based on its ride quality, and one such method used is response type ride quality measurements. If the old surface of the pavement is functionally inadequate, an overlay surface may be added to improve its performance. In cases where the pavement surface fails to meet one or more levels of service, a functional overlay may be necessary. The minimum thickness of the overlay surface for functional purposes will depend on factors such as construction convenience and the desired level of service.
Distress Surveys
To determine the extent and nature of damage to the existing layer, distress surveys are conducted. These surveys provide valuable data regarding the performance of the resurfacing layer. There are various methods employed for this purpose, but no standard method has been established as yet. The most commonly used methods are the Pavement Condition Index (PCI) and the Concrete Pavement Evaluation System (COPES), which are employed for flexible and concrete pavements, respectively. In the past, the Highway Pavement Distress Identification Manual was followed as a guide for these surveys.
Structural Adequacy
Non-destructive testing is a well-known method used to assess the structural adequacy of existing pavement surfaces. It involves analyzing the response of the pavement to applied loads, and there is a correlation between the nature of the response and the pavement’s structural adequacy.
AASHTO, or the American Association of State Highway and Transportation Officials, has developed another approach known as “remaining life.” This approach aims to estimate the amount of life that has been consumed from the pavement. This consumption can be measured based on time or the number of loadings. However, this method is not without its limitations, as errors in the measurement of remaining life can result in either a higher or lower value without any apparent reason.
To address these limitations, AASHTO has proposed a third approach that makes use of distress surveys and the material properties of the existing pavement. This method aims to determine the structural capacity of the pavement layer based on these factors. By taking into account the pavement’s distress level and material properties, this approach can provide a more accurate assessment of the pavement’s remaining life and structural adequacy.
The Structural Design of the Pavement or Floors for Resurfacing
When considering the comparison between structural and functional deficiencies in resurfacing projects, structural deficiencies will take precedence over functional ones. This is due to the greater thickness required to address structural issues as opposed to functional ones. Resurfacing thickness design can be approached in multiple ways, but certain requirements must be determined, such as the structural capacity needed to account for both current and projected traffic during the planned design life of the resurfacing layer. The effective structural capacity, or in-situ structural capacity, must also be calculated and compared to the overall structural capacity.
In addition to these capacity requirements, other factors must also be considered during concrete resurfacing projects. These factors may include addressing other deficiencies beyond just structural or functional concerns, such as improving the overall aesthetics or addressing safety issues. Additionally, the specific conditions and demands of the location must be taken into account in order to ensure a successful resurfacing project.
Interface Between Concrete Layers
The area between an underlying layer and an overlay surface is crucial to consider in design. The interface between these two layers determines the nature of the bond, which ultimately affects the performance of the entire resurfacing layer. Interface materials serve two primary purposes: to improve the bond between the underlying and resurfacing layers, or to act as a separator between the two layers. The former purpose creates a monolithic behavior between the layers, meaning they act as one under load action and transfer. The latter purpose results in separate elements, with little to no connection between the two layers. This distinction gives rise to two types of resurfacing: bonded and unbonded.
Bonded Resurfacing
Bonded resurfacing is a process that involves the use of plain cement concrete slurry or grout to create a bond between an old and a new layer. The grout used for this purpose is prepared in a mobile mixer and typically comprises of Portland cement and water. It is important to maintain a water-cement ratio of no more than 0.62 for optimal results. However, in certain areas, this method is not employed, and instead, the resurfacing material itself serves as the bonding interface material.
Before applying the resurfacing material, the surface needs to be cleaned thoroughly. The application of the resurfacing material is then done on the clean surface. The main benefit of this technique is that it has been found to be highly effective in improving the bond between the old and new layers, leading to increased durability and performance of the surface.
Overall, the use of bonded resurfacing with plain cement concrete slurry or grout, or the resurfacing material itself as bonding interface material, has proved to be a reliable and efficient method for improving the performance of surfaces. Proper preparation of the grout and thorough cleaning of the surface before applying the resurfacing material are essential for achieving optimal results.
Unbonded Resurfacing
Unbonded resurfacing is a technique used when the underlying layer is weak and highly distressed. When a bond is made between the new overlay and the old layer in such conditions, reflective cracking is likely to occur due to the transfer of stress from the weak bottom layer to the new top layer. To avoid this problem, an unbonded interface material is used, allowing the two layers to perform individually. Several materials are available for this purpose, including asphalt-aggregate mixtures, polyethylene, wax-based curing compounds, and liquid asphalts.
Initially, a liquid asphalt layer covered with a polyethylene sheet was the preferred method for creating an unbonded surface layer. Thick layers of surfacing are recommended over thin layers, as thin layers can also increase the risk of reflective cracking in the overlay. The recommended thickness of the asphalt layer varies depending on the condition of the underlying pavement.
If there are joints or cracks greater than 6mm and significant deterioration of slabs and spalling, an asphalt layer with a thickness of at least 25mm should be used. For less severe faulting and slab deterioration, a thin layer of asphalt with a maximum thickness of 13mm or a slurry seal material with a nominal thickness of 3mm is recommended to cover all surface defects. If there is no evident fault or cracks, a slurry seal with a minimum thickness of 3mm or an asphalt layer followed by a sand cover can be used.
It is crucial to ensure that the thickness of the layer is adequate to prevent keying of the overlay. If the layer is too thin, it may not be able to perform its intended function effectively.
Fig.1: Before and after providing interface material between the damaged and the new layer
Drainage for Concrete Surface
In order to ensure proper water drainage, it is necessary to include cross slopes in pavements. However, it is now also important to incorporate texture on the pavement surface to increase skid resistance. When resurfacing is done, it is recommended to provide subsurface drainage. During pavement evaluations, the designer should check for joint faults, pumping, corner breaks, and other types of distress, particularly in Portland cement concrete (PCC) pavements. For asphalt concrete (AC) pavements, fatigue cracking and potholing are common forms of distress. Any sign of moisture-related distress indicates inadequate drainage, so proper drainage should be established before overlay construction. Open-graded drainage layers can serve as a good interface material for unbonded interface layers.
Reinforcement for Concrete Resurfacing
Reinforcement in the form of distributed deformed steel is used in certain pavements to control different types of cracking. The cracking is primarily caused by joint spacing, which is influenced by the shrinkage resulting from the hydration reaction of Portland cement. The extent of shrinkage varies with temperature and the slab’s moisture content. The reinforcement used in resurfacing is similar to that used in new pavement installation, and the AASHTO 1993 provides comprehensive details on reinforcement design. For overlays joined through joints, the slab length determines the need for reinforcement. Slabs with a length less than 4.6m do not require reinforcement, while slabs with longer lengths need reinforcement with the cross-sectional area ranging from 0.05 to 0.20% of the slab cross section. In concrete reinforced overlays, longitudinal reinforcement is necessary to keep transverse cracks tightly closed, prevent the penetration of undesirable chemicals, and facilitate proper load transfer. The percentage of steel required in this case is higher than that used for jointed overlays, with a minimum of 0.6% of the slab’s cross-sectional area necessary. In recent practice, however, 0.9% of the cross-sectional area of the slab is used.
Joints in Concrete Floors and Pavements
Adequate joints are necessary in pavements to accommodate movements caused by temperature variations and changes in concrete volume. For plain cement concrete resurfacing, joint location and provision depend on the type of interface used. If a bonded resurfacing is employed, it must match the joints used in the underlying pavement layer to prevent reflective cracking on the new layer. Failure to do so would reduce pavement performance.
However, a different approach is taken when using an unbonded interface. It is recommended to have a mismatch of 0.6 to 0.9m for transverse joints in the surface when compared to the original pavement, but the joint must match with the one in the underlying pavement. This reduces stress concentration and related distresses, improving pavement performance.
Advantages of Concrete Resurfacing
Concrete resurfacing is an important part of maintaining and prolonging the life of a surface. It can help prevent the formation of cracks and potholes in driveways, for example, and can make them last longer. One of the benefits of concrete is that it has a light color that can help regulate temperature and keep surfaces cool during hot summer months. Additionally, concrete resurfacing can be done with staining techniques that offer a variety of colors and can add aesthetic beauty to a surface. With so many color options available, concrete resurfacing can be a great way to enhance the look of a home’s exterior.
Another advantage of concrete resurfacing is that it makes snow removal from the surface easier than it would be with other materials. The smooth, even surface of the concrete makes it simple to shovel snow off without getting stuck in cracks or uneven areas. All in all, concrete resurfacing is an excellent choice for those looking to improve the look and longevity of their surfaces, whether for practical or aesthetic reasons.
Disadvantages of Concrete Resurfacing
If proper evaluation and overlay procedures are not followed, concrete resurfacing may not be successful and result in visible cracks on the surface. In such cases, the only solution to remedy the problem is to completely remove the existing pavement and construct a new surface. However, this option may not be economically feasible for larger areas. Therefore, it is important to ensure that the evaluation and overlay procedures are done correctly to avoid the need for costly and extensive repairs. By taking the appropriate steps, it is possible to maintain and extend the life of existing concrete surfaces while minimizing expenses.