A flat concrete roof is one of the most complex and challenging building elements because it is consistently exposed to harmful agents from the external environment. Concrete flat roofs may consist of many functional defects, including cracking, disintegration, and others [1
]. As such, remedial treatments are necessary to improve the performance of concrete flat roof and to extend its service life [3
]. Remedial treatments are conducted not only on old concrete structures but also on newly constructed structures because of many influencing factors. Diverse industrial products have been developed to repair concrete flat roofs. However, building codes and standards for the evaluation of remedial treatments are yet to be established. Issues on questionable quality of remedial treatments have also been raised.
The performance of flat roofs has been studied. Carretero-Ayuso et al. [4
] identified the factors that influence defects and found that design is the most important parameter. Carretero-Ayuso and de Brito [5
] investigated the effect of third-party monitoring on flat roof construction and observed that third-party monitoring can improve the quality of flat roofs. Also, Conceição et al. [6
] developed a system to inspect, maintain, and rehabilitate flat roofs.
Remedial treatments on concrete have also received considerable research attention. Jumaat et al. [7
] reviewed the repair treatments for concrete beams and discussed the advantages and disadvantages of each repairing attempt, such as using cement grout, mortar, concrete, sprayed concrete or shotcrete, epoxy, ferrocement with mortar, fiber-reinforced polymer (FRP), and sprayed FRP. Bhaskaran et al. [8
] reviewed and compared the estimated cost of anti-corrosion approaches, such as Uhlig method, Hoar method, NBS-BCL input/output method, and the net present value method. However, the assessment methods for the remedial treatments of concrete flat roofs have yet to be investigated comprehensively. Garrido et al. [9
] compared and examined the performance of combined techniques to repair bituminous waterproofing and observed that heating is essential for repairing bituminous waterproofing. However, it should be noted that the above-mentioned studies mainly focused on technical issues and parameters, while not providing emphasis on the quality assessment of on-site remedial work. In this aspect, several techniques to evaluate and analyze the quality of concrete flat roofs have been looked into. In general, three types of assessment methods are applied in current practice: qualitative, quantitative, and semi-quantitative methods. Among them, the qualitative method is the most common, where surveyors or inspectors use their experience, knowledge, and intuition to evaluate the quality of concrete flat roofs. While this method can be convenient and straightforward, the findings can be subjective and different among individual users. Nevertheless, Walter et al. [10
] developed a checklist to identify the defects of a bituminous waterproofing system. Kenai and Bahar [11
] designed an assessment method for the new Algiers airport building with visual inspection, seismic parallel technique, and nondestructive equipment [12
]. Moreover, Mosa et al. [13
] developed an expert system to identify the causes of problems and their expected effects on pavement as well as applying suitable remedies.
Several techniques have also been developed to quantify the performance of concrete flat roofs. One of the most common quantifying methods is through laboratory experiments. In laboratory experiments, the effects of factors on the performance of a waterproofing system are examined. For example, Weigel and Stephan [14
] used Fourier-transform infrared spectroscopy (FTIR) and multivariate analysis methods to correlate the chemical and physical characteristics of bitumen samples, and their results are based on refineries, grades, and aging states to predict chemical, conventional, and rheological parameters. These methods provide highly accurate results, but they are expensive and may be unsuitable for existing buildings. Morgado et al. [15
] supported the approach of Weigel and Stephan [14
], and they found that the replacement of a waterproofing system should be undertaken earlier than the expected year (20 years) because damage mostly occurs in waterproofing systems. Skominas et al. [16
] performed a laboratory experiment to evaluate concrete mortar as a repair material for hydraulic structures. Furthermore, Che-Ani et al. [17
] monitored and controlled water ponding problems with etape-sensors. More advanced and novel quantitative techniques are those such as big data analysis, simulation, and modeling. Bailey and Bradford [18
] conducted big data analysis to examine a large army of roof inspection record and to identify defects and their impacts. Tamas et al. [19
] also developed a simulation model to select waterproofing rehabilitation for a church and a castle. These novel quantitative techniques can provide more accurate and precise results, but their implementation requires large and detailed data. However, most existing maintenance record systems of buildings are confidential and different among buildings. Other associated problems are like insufficient recorded data, especially for construction methods and materials that were used in old existing buildings, and numerous unauthorized structures that have been constructed. These uncertainties may increase the difficulties in evaluating the performance of concrete flat roofs.
Semi-quantitative assessment methods are uncommon in evaluating the quality of concrete flat roofs, but they are commonly used for fire risk assessments, such as fire safety rankings [20
]. Moradi-Marani et al. [12
] designed a similar method to investigate the corrosion damage and repair system in a concrete jetty structure, while Che-Ani et al. [21
] developed a condition survey protocol matrix to assess the condition of buildings, where they produced a checklist and assigned weighting to each attribute. They categorized the proposed condition assessment into five scales, i.e., as good, fair, poor, very poor, and dilapidated; and ranked the priority of maintenance work into four classes of normal, routine, urgent, and emergency. The semi-quantitative assessment method may involve some nondestructive equipment to provide precise data. Although the accuracy of its assessment results is lower than that of quantitative methods, the former is more convenient and user-friendly than the latter when analysis is conducted on site.
In this study, the authors have developed a semi-quantitative method to assess the quality of the remedial treatments on concrete flat roofs of multiple buildings, to save money and resources, and to prevent the possibility of performing the remedial treatment again in a short period. An ideal assessment method should be user-friendly, suitable for spaces, easily documented for future monitoring, accurate, and precise. The advantages and characteristics of the proposed method are similar to those of other methods to the features of ideal assessment methods. This paper highlights the problems and limitations associated with the existing remedial treatments on concrete flat roofs and discusses the development of a semi-quantitative assessment method to analyze the quality of the remedial treatments for concrete flat roofs of multiple buildings, where a 10-point weighting is calculated based on the results of ranking, and the score assessment scheme is developed.
This paper discusses the development of a semi-quantitative assessment method to evaluate the quality of remedial treatment for concrete flat roofs in multiple buildings. The overall procedure of the development is presented in Figure 1
Important information was collected first through a comprehensive literature review, followed by a preliminary study on the case with a performed remedial treatment, and an assessment of construction stakeholders. Subsequently, the repairing principles were identified based on the collected information, grouped, and verified through the assessment of experts. The experts involved in this process were from diverse backgrounds, such as researchers and academic staff, specialist contractors, consultants, and government staff. They had at least 2 years of working experience in dealing with concrete flat roof-related issues. This process was repeated unless (and until) all experts agreed with the grouping and verification of attributes. After that, the point-scheme was developed and obtained according to the analyzed results ranked by the experts. Finally, the assessment scheme was applied on a completed remedial treatment of concrete flat roof.
The assessment scheme was further revised according to the feedback of surveyors. The details of these procedures have been explained and discussed in Section 3
of the paper, considering that these procedures are part of the development of an assessment method for the evaluation of the quality of remedial treatment on concrete flat roofs.
4. Concluding Remarks
Concrete flat roofs are one of the building components that are most prone to degradation. Remedial treatments are necessary to extend the service life of concrete flat roofs. However, limited research has been conducted to assess the quality of remedial treatments of concrete flat roofs. In this study, a semi-quantitative assessment method to analyze the quality of the remedial treatments on concrete flat roofs of multiple buildings has been proposed. The development of the assessment method was initiated with the identification and grouping of repairing principles and assessment criteria, which were identified through literature survey, case studies, and interviews with construction stakeholders. Score values were assigned to the grouped principles after analyzing the assessment results and taking the opinions of the experts. The remedial treatment on a selected concrete flat roof was assessed with the developed assessment method. The assessment method was further revised according to the feedback from the surveyors.
The proposed method is advantageous compared to other quantitative methods. It is user-friendly and easily applicable. Also, it does not require expertise to assess the quality of the remedial treatments of concrete flat roofs. However, the results from semi-quantitative methods can be less precise and accurate compared to quantitative methods. However, this technique may provide a more precise and accurate results than qualitative methods, which are subjective and may vary based on the prediction of users.
The performance of the remedial treatments of concrete flat roofs can be appropriately examined with the proposed method. Through this approach, it is practical for stakeholders, especially non-experts to understand, monitor, and control the performance of remedial treatments of concrete flat roofs. This process can prevent the wastage of resources and time, and even minimize the safety hazards to building users and their valuable properties. However, this method is unsuitable for remedial treatments of other building components due to varying repairing principles, factors, conditions, and materials. Further research is required to comprehensively study the influencing factors and performance of the remedial treatments of other building components.