An analysis of the performance of demolition with least cost,
minimum time and available cost-effective technology
Abstract:
This paper investigated the efficiency of selective demolition of structural concrete in respect to cost, time and uses of technology in the process of constructing the pedestrian ramps where the reinforced piles and pile caps have been reused from the earlier stairways which were replaced by the ramps. The traditional technology was used as the high technology was not feasible for the small and medium projects. The cost and time of the selective demolition of structural concrete were higher than the regular demolition of concrete. In the near future, it is apparent from the research results that the higher time and cost would continue as the construction industry is less adaptive to the advanced technology due to lack funds and incentives.
Keywords: Structure, concrete, technology, efficiency, cost.
1. Introduction
The selective demolition of concrete for a renovation project is very common in the architectural renovation projects of buildings, transportation projects like bridges and pedestrian ramps, and other similar projects. The purpose of the selective demolition is to reuse the existing concrete structures into the new renovated projects. The benefits of reusing such structure allow for recycling of exiting projects’ elements, reduction of construction materials resulting in a smaller carbon footprint, and less cost for the projects. Reusing materials are environmentally sustainable and financially viable.
Though the selective demolition is very beneficial and desirable, there are problematic issues related to the process of selective demotion. Some of the issues are the use of the manual labor incentive technology which increases labor cost and time for the demolition process, less precise technology for demolition of structurally sensitive structures, and lack of incentives of using current state of the art technology like robot or automated technologies.
This research project will investigate the causes of such problems in the light of current literature on the issue of the selective demolition. The data and information will be used from the project for activity and operation of the selective demolition of slabs on existing pile caps of pedestrian stairways to reuse the piles and caps for construction of pedestrian ramps. The analysis will recommend how the present problems can be approach with efficient and cost- effective method of selective demolition of concrete for the construction project.
2. Research Scope and Objectives
As mentioned, the scope of the research includes demolition of selective concrete slabs and pile caps of two existing stairways for beach and boardwalk access, and reusing those piles and pile caps for the construction of two pedestrian ramps for waterfront access of a New York City project.
The objectives of the paper are several. First, to document the exiting methods, technology, and cost involve in the structural concrete demolition as applied in the pedestrian ramps project. Second, to determine what existing methods technology that existed could be used for the pedestrian ramps project with cost effective manner. Third, to determine the factors that contributed why other methods or technology were not used. Fourth, to compare the existing costs of labor and technology, and advantages and disadvantages of such methods or technology.
Figure 1: Project site with red mark
Figure 2: Typical Boardwalk. Ramps for getting on Boardwalk from the Street.
Figure 3: Location of construction site along the Rockaway Boardwalk and Beach
Figure 4: Demolition plan of existing structures
Figure 5: Concrete demolition of existing stairways
Figure 6: New ramps construction section
3. Literature Review (Theorical Basis)
Demolition is a part of the overall construction industry. But the construction industry considers the renovation projects with less importance than the construction of new projects. The literature is divided into four areas (though there are overlaps): a) book and journals, b) publication of professional and trade organizations, c) government codes (city, state, and federal), and d) construction industry’s practices and publications. The following is an analysis of the theory of research literature to the present topics.
3.1 Books and Journals
Here presented are the reviews of books and journal articles of academic interest, though there are discussion on books and publication in the later section of professional, trade and construction industry sections.
For inspiration of reusing the materials and structures where ever possible for the reducing of carbon footprint, the Public Architecture printed a book as primer. The book gives examples of different renovation project. (Public Architecture 2010).
One of the major recognitions by the American Institute of Architects (AIA) is the publication of Building that Last: Adaptability, Deconstruction and Reuse, which recognizes that small and medium architectural projects demolish some structures during demolition and reuse part of the existing structure in renovated projects (American Institute of Architects 2020). The publication has acknowledged that the renovation of apartments and houses are important projects for the architectural professionals and are ongoing in the built-up cities like New York.
The adaptive reuse of concrete in renovation project is getting momentum. “By definition, adaptive reuse is characterized by the DNA of an existing host structure and, with it, the physical evidence of a previous user or users. This physical evidence is found in renovation, refurbishment or extension with the demolition of any part of the existing structure.” (Wong 2016) Though there is momentum growing there is lag of proper regulation and guidance for concrete demolition industry. “Current building demolition is severely restricted by numerous factors, and its evolution by necessity must involve the demolition industry, regulations, economics, new
technologies and management and so on. In general, compared to the construction regulations, demolition regulations are still rather separate, roughly-outlined and out-dated. There are no standards for demolition contractors and procedures.” (Pranab 2015).
3.2 Publication of Professional and Trade Organizations:
The theoretical analysis of the selective concrete demolition is undertaken by the design and construction industry in different manner as demolition is not considered major construction activities. But for small scale project it has been recognized that selective demolition is very important to reuse and recycle the materials. Selective demolition is the part of renovation of an apartment or condo, a house, or any building as recognized by the American Institute of Architect. Its recognition has mentioned above (American Institute of Architects 2020).
The American Society of Civil Engineers (ASCE) did not have any significant provision in its code about the demolition of concrete. But it has sponsored different seminars and conferences about demolition and reuse of concrete structures. Also, its affiliates and other engineering societies have seminars and publication on the demolition of concrete and reuse of the part of the structure for renovation. (London Concrete Society1985).
Another example of the seminar about the demolition by professional organization (Lauritzen and Petersen 1991).
The American Concrete Institute (ACI) has published several books on construction of concrete structure but the demolition process is not elaborated in any of its publication. It has some publication about reuse of concrete during new construction. ACI is more interested in new construction of concrete as vast amount of concrete is used in the construction of concrete structures. (American Concrete Institute 2002; American Concrete Institute 2023).
The American Concrete (ACI) has manual for the concrete mixing, pouring and maintenance but it has no specific guideline for the selective demolition. But it has to aware that the repair of concrete is a major issue but it does not take an extensive demolition of concrete. (American Concrete Institute. 2019).
3.3 Government Codes (City, State and Federal)
The government code is important in the construction industry. The level of government involvement is to regulate the safety and public health of the community. The three types of governments are involved in the regulation of the construction industry. These are the local (city, county and township), state and federal government.
For construction, the federal level code is mostly used through the Environmental Protection Agency (EPA) and Department of Energy (DOE) through encouraging the reuse or recycle of construction materials with energy efficient construction method. (U.S. Environmental Protection Agency 2015).
The state level code is mainly the adoption of the International Building Code which the local governments adopt with the curtailing suiting to the local area. (International Building Code (ICC) 2021)
The local government level codes are intensive and include directives and regulation for the construction activities, duration of work, safety, site locational guidelines and construction methods. These are codified in the construction, energy, building and other related legal documents. Construction and fire code are also related to safety. The local government may dictate the safety and demolition method. It may not allow the automated machine in selective demolition of a building, explosive or impact ball for concrete demolition in residential and commercial areas. Effecting the noise and vibration of nearby structure is regulated by the local government. New York City has extensive regulation of these codes. (New York City Construction Code 2023; NYC Building Code 2022; NYC Fire Code 2023).
3.4 Construction Industry’s Practices and Publications
The construction industry has some regulatory and standard organizations. One of these is the Construction Specification Institute (CSI) which MasterFormat is well known categorization of all construction activities in different codes or specification. All major professional organizations, like American Institute of Architects and American Society of Civil Engineers follow this MasterFormt for preparation of construction specifications and documents. Also, all contract work for construction of government and private projects follows this MasterFormat. (Construction Specification Institute 2023).
The following is the partial breakdown of activities of demolition in the MasterFormat.
03 05 00 Common Work Results for Concrete
03 05 05 Selective Demolition for Concrete
04 05 00 Common Work Results for Masonry
04 05 05 Selective Demolition for Masonry
05 05 00 Common Work Results for Metals
05 05 05 Selective Demolition for Metals
The construction industry which is responsible for the demolition of the concrete structure usually uses common traditional practice of demolition. The sporadic trade publications in the form of construction companies’ work methods provide may information of the informal method of construction work undertaken by construction industry. (DeFoe 2023; BigRentz 2019).
In the current practice, the automation or robotics system is not used for the small demolition project. The company which uses higher level of technology have more technical internal publication. (Husqvarna 2023; Jebelli et al 2020)
5. Demolition Methods and Efficiency
5.1 Demolition Methods
There is different equipment used for the demolition of concrete. The traditional hand equipment to high end technology including the robot. In this project, two types of equipment are used: hand-held jackhammer and backhoe’s blades.
Figure 7: Jackhammers with different accessories.
In Figure 7, the different types of jackhammer bits like breakers, chisels cutters, and spades bits are shown. These are needed to skillfully remove the concrete to maintain the structural integrity of the reusable concrete.
Figure 8: Uses of backhoe with blade to demolish the slab on the pile cap
Figure 9: Use of blade of backhoe to break concrete on a pile cap.
Figure 10: Example of using backhoe to break concrete around pile cap
For reinforced concrete buildings, jack hammers are commonly used to break down concrete (Figure 7; Figure 8). “For reinforced concrete … jack hammers are commonly used to break down the concrete.” (Pranab 1015).
As the major portion of the demolition was reinforced concrete slab and pile caps, the traditional method of jackhammers was used. Jackhammers were more labor intensive and take more time. It is used in small area where the backhoe cannot have access or where the careful precision demolition was done like at the tip of the pile cap which is structurally very sensitive.
5.2 Efficiency of Demolition of the project
Efficiency is counted through the amount of force required to break the structure of concrete, like slab, beam or pile. The rigidity or structural strength of a concrete structure may not be known. For example, different force is required to knock down a 3,000 psi concrete than a 6,000 psi concrete structure. As in most cases, no data for an existing structural strength is known for a structure to be demolished.
But electronic forensic method can be used to determine the concrete strength to choose proper equipment to demolish. This is not used in this project. Current project used the trial-and-error method. First, bigger bulldozer was brought, then hand drilled machine was brought, and then smaller bulldozer was brought. No specific plan could be made without knowing the proper strength of the elements of structure to be demolished.
The efficiency is generally measured in respect to the performance of the different aspects of the project, such functional, formal or physical, cost, time quality and reliability. But this research particularly emphasized on the investigation of cost time and reliability.
Figure 11: Steel bars from the exiting slab on the reusable
pile caps. The slab was built with very high strength
concrete and required extra care during demolition,
so that the reusable pile cap is not damaged.
Figure 12: After broken concrete and reinforcement was removed,
the view of reusable pile cap one of the ramp sites. Still slab on the pile
cap need to demolished
Figure 13: View of two reusable pile cap after concrete slab demolition
6. Findings and Results
The findings and results can be described on the following attributes which are mentioned in the earlier section.
Functional Performance: The result of the proper functional performance is the product rate. If the operation or process worked properly, the production rate would increase. For proper functioning, the materials should be supplied on time, work scheduled should be properly coordinated, appropriate equipment should be functionally integrated with crews and critical path of project scope should be followed.
Formal/Physical Performance: Particularly for the selective demolition project, the proper monitoring should be done for saved part of the structure, so that its structural integrity is maintained. So, proper use of equipment and applied force on the structure should be selected. Proper space for the manipulation of equipment needed for this purpose. The project site was very narrow and movement of equipment was limited. So, performance was hampered for demolition but proper size of equipment is necessary to work in limited space.
Cost Performance: Using of less labor, equipment, and materials, and other cost is desirable in project. The demolition cost is given in the construction contract was as follows:
Demolition of reinforced concrete
Demolition of general concrete
Demolition of paver concrete
Demolition of railing, deck and wood.
For concrete, the payment was made per cubic yard of concrete broken. but the efforts and resources used for the high strength concrete breaking took longer time than low strength concrete. So, there was tension among the demolition subcontractor, general contractor and the owner of the project about quantity of materials and payment amount.
The demolition cost is about 8% of the project costs. The demolition items included the reinforced concrete stairway, abandoned pile and pile cap, paver concrete, recycled wood deck, and metal railing.
Time Performance: The project duration is for one year from the initial setup to the handover of the completed structure of ramps. The mobilization and demolition are accounted for nearly two months. After the partial demolition, the site would be ready for new piling and construction work.
Quality/Reliability Performance: The quality assurance and quality control of the project was regulated by the construction drawings and specifications, New York City building and construction codes, and the federal, state, and city’s environmental regulations. The general contractor followed the procedure and process to use proper materials and methods. The designers make regular visit as needed to verify quality of performance. The city’s project engineer or manager oversaw the quality on daily basis. (Kasai 2023).
Figure 14: Clear view of a saved reusable pile cap. It shows the
quality and demolition work
Safety/Security Performance: The safety and security performance can be achieved by following:
- Properly securing the site from outsiders during and after work hour. Lock should be used after work hour to close the gates.
- Safety of workers, public or pedestrians, any visitors, delivery people, and utility crews should be properly monitored and executed.
- Heavy trucks may pose danger to people on site, so trucks should be properly guided.
- Emergency medical kits should be kept on site.
- Proper use of personal protective equipment (PPE) should be implemented.
- There should be site safety plan and at least one individual should monitor it.
Figure 15: Narrow workspace and safety risks.
Risk Performance: The mitigation of risk can be done by performing the following activities:
- Properly securing the construction site by fencing and installation of sign.
- Acquiring required permits from the planning, building, and transportation departments and properly exhibiting them on site.
- Proper investigation of whether there are underground utilities lines which may be damaged during construction process.
- Securing storage and site office.
- Controlling the visitors.
- Regulating public and pedestrians during demolition and construction time.
- Monitoring severe weather condition, so that construction process and workers are not at risk.
As the emphasis of the research is on the cost, time and technology, in the following these three issues are discussed further in respect to the research results.
Cost: In general, the cost of selective concrete demolition is higher than the demolition of whole building or structure. Though the contractor did not want provide the cost data for privacy purpose, comparing the similar project of the contractor, it was found that the labor and technician of the demolition project were highly paid.
The costs of labor for the selective demolition of the ramp project to run the equipment are higher than the regular demolition of a complete structure. Though the costs of general labor are not that of a big difference per head of labor but number of labors need were higher. The higher cost of labor was involved in the case of foreman and operator of the equipment. For the operator, to break the reinforced concrete where some part would be saved for further use in the construction project, the operator has to be knowledgeable about the structural engineering and mechanics. So, one of the operators have college degree and training in structural functioning of the elements of the structure with 25 years selective demolition experience. His fee was three times higher than the regular operator. A high-level trained operator is employed for the reason that the general contractor cannot take risk of damaging the part of the structure which need to be preserved and reuse. For any substantial damage of reusable structure would hamper the continuation of the project.
Time: In construction project time is essence as a project need to be finished within the time duration. In this project, the time allotted for selective demolition could not be maintained. The time for the project took longer than the comparable project where the whole structure has been demolished. The part of the project where the structural concrete need to be demolished, it took twice as much time of comparable regular project. In general, the demolition contractor does not have specific information about the strength of the concrete. It goes on assumption by just looking at the concrete or with few hits by hammer to determine the strength. Based on that the equipment was selected. At one stage, when a small portion of the concrete slab was left which was not suitable for structural safety to break with the large backhoe as slab was on the top of a file cap, the contractor decided to break that slab concrete with the jackhammers. Also, some of the existing vertical rebars coming out from the existing pile cap need to be saved when the exiting slab is broken. The rebar would act hooking the pile cap with the new slab. (Figure 14). It is an important structural function to provide the integrity of the old and new part of the structure to be continued as a structural unity. So, the big backhoe was
returned and a jackhammer was rented. But when tried to break with jackhammer, it was found that the strength of concrete on the pile cap slab was much higher than the slab of the other part of the structure. In the process, the backhoe’s blade was broken. It was not possible to break the slab concrete with the jackhammers and in the process of trying to demolish slab concrete few blades of the jackhammer were damaged. So, the contractor made the decision to rent a smaller backhoe which was able to access to the all part of existing slab and broke the concrete with required force and impact. This event delayed the demolition process for few days with additional cost.
Technology: The technology has been used for this project was similar to the comparable project of a complete demolition project would have been used because of the size of the selective demolition. Also, the availability of the rental equipment and skilled labor for the operation of the equipment are available. Though the technology of jack hammer and backhoe blades have been used nearly a century by construction industry, there have been development of high-end technology which discussed earlier.
The above-mentioned high technology may be more efficient in respect to time of demolition but the availability of such equipment and operators, and cost involved were not reasonable. The reasonableness is assumed from the cost in design and bidding documents, actual bids, comparison of bids, and availability of subcontractors with available technology that wanted to use in the project.
No assessment has been made whether the higher technology-involved projects were better in respect to costs, time and cost-effectiveness of technology because such opportunity were not available in the current project.
7. Conclusion
For small and medium sized renovation projects, traditional and less advanced technology are common to use in selective demolition projects. For medium- and large-sized projects, the selective demolition involved more money, higher technological equipment with more demolition effectiveness like impact ball, large bull-dozer, pneumatic equipment, pressurized water, and even a robot can be used in special cases. But these involve higher cost which was not possible for this project. As it is apparent from the research, we know that there are no guidelines for what procedure to follow in a concrete demolition project including the proper pre-plan, selection of demolition equipment, and the choice of technical expert and technician, foreman and labor are different for the size and budget of every project (Pranab 2015). Usually, the general contractors rely on experienced demolition subcontractors for the advice and direction of using the equipment.
The finding of the project conforms to the existing knowledge about the cost, time and technology choice of the demolition project. The cost was higher, the time was longer and the traditional hand-held and low technology of back-hoe blade were used. Even the backhoe hammer or ball was not used to demolish in fear of damaging the reusable structure, only backhoe blades were used. Some lesson learn from the projects are that the carful verification of the strength of concrete and what type of equipment are suitable should be determined before the pre-planning stage of breaking the concrete. But the problems arises when the strength of the concrete is much higher than predicted by the subcontractor and the equipment order are not suitable to break the concrete. As the exiting reinforced concrete structure was built many years early, the blueprints or the specifications are not available. In most cases, the demolition subcontractor determines the
strength of the concrete through the trial-and-error method. For example, try one equipment, if it works, it is fine. If it is not, then the strength of concrete is assumed higher and subsequently suitable machines were brought.
As the project sponsored was the New York City which is also the regulator of the city’s construction, building, zoning and energy codes. So, as a city owned project, the city has provided leeway for completing the project. But if the project was owned or sponsored by private organization, the delay would have been longer. For example, the discovery of an existing concrete wall underground about 20 feet long parallel to the ramp were not mentioned in the city’s planning and design documents. When and why that wall was built could not be ascertained. Whether there was some purpose of it according to geology or subsoil condition was the general comment. The city after deliberation ruled that breaking up the wall with minimum disruption to facilitate the construction work was not harmful to soil or the environment. The city quickly made the decision. The decision would have been taken longer if the project was privately owned or sponsored.
There was not enough literature and incentive for research for concrete demolition in the academic area and professional organizations. As the recycling and reusing of concrete structure are environmentally viable, less materials are used, generate less carbon, and economically beneficials, then more research is needed in respective areas.
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