Comparison of the actual costs during removal of concrete layer by high-speed water jets

This paper describes the process of possible evaluation of costs of using high speed water jet technology for concrete removal methods. High speed water jet technology is a progressive technology of removing damaged concrete used in civil engineering since the 80's of 20-super-th century. It has been changing and developing since that time. But there is little information in literature devoted to the economic evaluation of this technology. Detailed economic analysis is still missing. This paper aims to compare comprehensively in economic terms the costs of removing concrete using the technology of both continuous oscillating and pulsating oscillating water jets. The research was realized in cooperation with research institutions and industrial companies and was supported by state budget of the Czech Republic and from the European Union. The scheme of cooperation of the University, research institutions, industrial companies and government follows the Triple helix model.


Introduction
Renovation of concrete structures represents a great part of total turnover of construction industry worldwide. Removal of degraded surface and preparation of surface for renovation materials are very important. As cost of energy and the input of materials grow, it is necessary to look at ways of decreasing cost of removal of degraded concrete. Therefore, it is necessary to choose an optimal and cost effective way of removal of disrupted layers of concrete. The first step towards this goal is to specify the cost of possible ways and technologies of concrete removal for purposes of renovation.
Various types of concrete removal methods can be used. As removal of degraded layers of concrete is costly and ecological aspects are becoming more important than ever before, new technologies with low environmental impact are being developed. Driven by cost, need, and limited resources, the technology for concrete removal is rapidly advancing. Partial removal of critical structural components for repair rather than replacement, geographical constrains, access to structures planned for removal, environmental regulations, and worker and structure safety will continue to effect an evolution of developing methods and equipment (ACI 555R-01 2001). ACI 555R-01 Removal and Reuse of Hardened Concrete state these basic methods for removal hardened concrete: • hand tools; • hand-operated power tools; • vehicle-mounted equipment; • explosive blasting; • drills and saws; • nonexplosive demolition agents; • mechanical splitters; • heating and thermal tools; • and hydrodemolition (water-jet blasting).
Total cost of removal of hardened concrete can be sumarized as costs for removal method, partial or complete concrete removal, reuse, transportation and waste disposal, and additional inspection and testing (ACI 555R-01 2001).
This paper describes the process of possible evaluation of costs of hydrodemolitionusing high speed water jet technology for concrete removal methods. The key event is the creation of an entrepreneurial university, whether from an existing academic base or a new foundation, which takes initiatives together with government and industry in creating a support structure for firm formation, regional growth and increasing the competitive advantage of economic development (Etzkowitz, Klofsten 2005).

Research of high speed water jet technology -cooperation of important institutions and practical use supported by the Government
'Triple helix' model indicates a relationship among academic authorities, industry and authorities as a merger of overlapping areas reflecting an impact of each element on other spheres. There are three main the most common configurations of the 'Triple helix' model: in the first model the areas indicating elements of the industry and academic public exist independently, without any interaction, and the dominant role of an intermediary is played by the authorities being the only element ensuring relations between the sectors; the second model shows interactive relations of different elements; the third model indicates close cooperation among separate institutions of science, business and government (Chlivickas et al. 2009).
Mentioned subjects (Faculty of Civil Engineering, Brno University of Technology, Institute of Geonics AS CR, v. v. i., and NET Ltd.) strive to create the third type of Triple helix model for effective cooperation and to reach innovation in the field of water jet. The third model of 'Triple helix' is the most successful model for high technologies development. This type of Triple helix model shows the highest degree of cooperation among authorities, industry and academic public as the configuration of 'Triple helix' model allows solving all problems in implementation of innovations (Chlivickas et al. 2009).
During solving the problems of high speed water jet technology, the research team registered the following national and international patents:

High-speed water jet technology
High-speed water jet represents a technology that is able to disintegrate even the hardest materials due to high energy transmitted to extremely small area (see e.g. Summers 1995). If we use water jets, there is no mechanical tool-material interaction in the process of disintegration. The erosion capability of the jets is widely used for many applications in modern industry. Water jet technology achieved significant progress during last decades in applications such as cutting of wide range of materials, surface cleaning, removal of surface layers and repair of concrete structures. Nowadays, a number of commercial high pressure systems are available on the market, some of them generating pressures up to 400 MPa, other delivering up to hundreds liters of water per minute. Water jet cutting and/or cleaning equipment except the pump is lightweight and the whole cutting process can be easily automated. The technology is also very advantageous for the removal of damaged concrete layers from buildings and structures (Hela et al. 2010). The jet is able to remove the damaged layer selectively without the introduction of any additional cracks to construction (in contrast to traditional technologies like jackhammering, grit blasting, milling etc.). Moreover, adhesion strength of coatings applied on surfaces prepared by water jets safely comply with values specified in relevant standards concerned with concrete surface treatment prior to repair (Silfwerbrand 1990).

Hydrodemoliton (= concrete removal and cleaning)
The first serious approach to the use of water jets for concrete hydrodemolition was probably that of McCurrich and Browne (1972). The first commercial hydrodemolition unit was finally developed and introduced after 10 years (Momber 2005). Hydrodemolition uses high speed water jet technology. High speed water jet technology is a progressive technology of removing damaged concrete used in civil engineering since the 80's of 20 th century. It has been changing and developing since that time.
Equipment for high speed water jet technology ranges from hand-held tools to large tractor mounted units and robots.
The effectiveness of a particular system depends on: • Nozzle type; • Nozzling pattern and distance to surface; • Water pressure; and • Contact time.
The nozzle is moving rapidly and continually over the area of removed concrete, and excess water is allowed to drain away (ACI 555R-01 2001). The high speed water jet technology makes its destructive action by means of three separate mechanisms: • Direct impact; • Pressurization of crack; and • Cavitation (Medeot 1989).

Economical aspects of high-speed water jet technology
There is little information in literature devoted to the economic comparison of the new technologies with traditional ones. Most of the contributions are dealing with cutting technologies, which occupy the largest volume of applications relative to the others. One of them dealing with the economic analysis of lumber processing systems was published by Manetsch and Huber (1993). Krastel and Drechsel (1999) tested the economy of lasers integrated in a cutting machine during material processing. They realized complete processing of a workpiece with different technologies in one setting. Rather successful comparisons of non-conventional techniques for material cutting are subject in the model by Vidová (2007): costs evaluation and costs analysis is based on measurement of economic effectiveness of the performance of different cutting machines.
Regarding the water jet technology, most of authors interested in the comparison of the advantages of water jet technology with other technologies concentrate solely on the observation of a typical parameter of the technology and on the basis of such analysis then predict the economic advantage or inconvenience. Axinte et al. (2009) used abrasive water jet turning to profile and dress grinding wheels. It was found that grinding wheel can be roughed and semi-finished at considerable lower time compared to that required for employment of conventional (e.g. mechanical) dressers. However, the authors do not address the total cost of the manufacturing process associated with water jet technology and mechanical preparation of grinding wheels (Sitek 2009). Sitek et al. (2009) referred to the research on disintegration of surface layers of corroded and non-corroded concrete by high-speed flat water jets. This type of water jet innovates continuous water jet. Results indicate that progressive type of water jet -so called pulsating water jet -achieved higher efficiency in comparison with the corresponding continuous one in every case. Improvement of the technology follows from the fact that impact pressure generated by the impact of bunch of water on a target is considerably higher than corresponding stagnation pressure generated by a continuous jet under the same operating conditions. Unfortunately, detailed economic analysis is missing again. Study on money saving using pulsed water jet was published by Yan et al. (2004) in the paper on delaminated concrete removal by forced pulsed water jet. The use of pulsed technique resulted in saving of $200/m 2 compared to the techniques used earlier (chipping and sandblasting).
Thorough economic analysis of the costs of water jet technology was presented for example by Zeng and Kim (1993). They developed a method for cost prediction of abrasive water jet kerf cutting based on the application of the predicted cutting speed. Their analysis was utilised in the study of Singh and Munoz (1993). They point out that unlike other technologies, using of water jet can save anywhere from 10 to 30% of total operating costs. They highlighted that economic analysis of the water jet cutting process is somewhat difficult due to three factors: a) the same cutting results can be achieved by many different combinations of cutting parameters, b) the process flexibility, its ability to cut different profiles without hardware changes, is hard to evaluate in most cases, c) different customers have different objectives and they may evaluate various attributes differently. Thus a good economic analysis model should account for these three factors.
This paper aims to compare comprehensively in economic terms the costs of removing degraded layers of concrete road panel using the technology of both continuous oscillating and pulsating oscillating water jets. To generate a pulsating jet, much cheaper equipment (up to 2.4 times) can be used compared to the equipment for generation of continuous jet preserving the same disintegration effects. But what are the actual operational costs?

Experimental procedure and arrangement
Current study is focused on both continuous and pulsating water jet removal of degraded surface layers of standard road reinforced concrete panel stored at normal outdoor exposure (influence of frost and atmosphere vapours, no chemicals) for approximately 18 years. To determine real volume of disintegrated material, the following types of high speed water jet were used: continuous oscillating and pulsating oscillating jets. A layer of concrete from a concrete panel was removed by means of these two technologies.  ), much cheaper equipment can be used to do the same work using pulsating technique. Moreover, since surfaces prepared with pulsating water jet demonstrate higher roughness and unevenness compared to the ones treated by continuous jet, better adhesion of coatings and/or repair mortars to substrates prepared by pulsating jet is expected (Sitek et al. 2002). During experiments several couples of treated surfaces with approximately the same value of disintegrated volume were compared to one another. Example of appearance of two compared surfaces is shown in Fig. 1.
Computational model based on the model presented by Vidová (2007) is completed by specific parameters used during the evaluation of technology of high-speed water jet, as formulated by Zeng and Kim (1993) and Singh and Munoz (1993). The model comes from assumption that total technological costs are the most important technicaleconomic indicator of the operation of machinery and equipment and also a suitable criterion for the comparison of variant solutions.
Total technological costs C total are specified as the sum of total fixed costs C fixed and total variable costs C variable . Let's consider the hourly costs for removing the concrete layer. Total costs related to labor hour can be expressed as In fixed costs C fixed , there are included depreciations of production equipment C depr , interests related to security of funds for equipment purchase C int , rent for production area C rent and possibly insurance premium for production equipment C prem : In variable costs C variable there are included material costs C mat , costs for workers' wages C wage , consumed energy C energy , consumed assistant substance C exc , consumed spare parts and consumables C spare , and costs for maintenance and repairs C main Structure of total costs items for computation model is demonstrated in Fig. 2.
Breakdown of items for calculation of total fixed costs and total variable cost for computation model are given in the following Table 1.

Results and discussion
The results of the calculations clearly indicate that the use of advanced technology of pulsating water jet can reduce significantly the cost of the process of removing layers of damaged concrete in comparison with traditional methods of concrete removal by continuous high-speed water jets. While the same volume of concrete is removed, the total hourly costs are at least 1.6 times lower using pulsating jet. At higher pressures and water flows (resulting in higher amount of disintegrated concrete per unit time), the use of pulsating technology further reduces costs; the ratio reached 1.8 in our tests. Since both technologies are similar (based on the same principles), the use of pulsating jets yields greatest savings compared to the continuous ones in depreciation items covering total price of the equipment and related costs for repair, maintenance and spare parts. Also energy costs are lower when using pulsating jets. The paper is a contribution to cost evaluation and costs analysis of water jet technology. This paper aims to compare comprehensively in economic terms the costs of removing degraded layers of concrete using the technology of both continuous oscillating and pulsating oscillating water jets. The presented computation model is based on the model of Vidová (2007), completed by specific parameters used during evaluation of technology of high-speed water jet technology as formulated by Zeng and Kim (1993) and Singh and Munoz (1993). This new model comes from the assumption that total technological costs are the most important technical-economic indicator of the operation of machinery and equipment and also a suitable criterion for the comparison of variant solutions.

Conclusion
It should be pointed out that this particular example cannot be applied generally. It cannot be claimed that pulsating jet technology is more economical than other technologies considering wide diversity of applications where water jet is used. It is necessary to evaluate an actual case and then decide to apply one or the other technology. Regardless, it should be taken into account that pulsating jet technology is becoming a serious competitor to relatively widespread continuous jet technology in many areas.