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Development and demonstration of energy efficient system for accelerated curing during repair and refurbishment of concrete structures

Final Report Summary - MCURE (Development and demonstration of energy efficient system for accelerated curing during repair and refurbishment of concrete structures)

Executive Summary:
MCure project had been initiated by the 4 SMEs from different European countries who are all committed to participating in the successful research, development and subsequent demonstration of an efficient curing system in order to improve the quality and curing time of concrete constructions and repairs. This research and technological development addresses wide concerns in construction sector as over 50% of expenditure in the EU construction sector is on repair of existing structures rather than on new build. The focus is chosen but is not limited to concrete, because the primary material of construction requiring repair in EU is concrete.
In terms of economic figures, the annual cost of repair of reinforced concrete structures in Western Europe is in excess of €5 billion, a problem which is likely to be even greater in Eastern Europe. Wide scale research undertaken by EU FP5 project CONREPNET 2004 showed that 25% of structure owners are unhappy with the performance of the repair within five years after the rehabilitation of reinforced concrete structures; 75% are dissatisfied within ten years. This has generated a requirement to deliver more durable and effective repairs to concrete structures. To meet this requirement, this MCure project will scientifically develop a novel accelerated curing approach which will improve the durability, accelerate the curing and consistency of concrete repairs, independent of climatic environment. It will be an energy and time efficient curing system. It will make more efficient use of resources, especially in harsh winter weather conditions due to the system robustness and the effectiveness of the technology in all kinds of weather. This approach will improve the productivity and competitiveness of SME repairs contractors. This technological approach will involve advancements in the fields of remote moisture sensing and concrete compressive strength.
Within this project, a team of scientist and engineers at Fraunhofer IGB together with project partner ERS has designed, developed and integrated a MCure-prototype which includes an optimum energy coupling mechanism, a driving system to repair materials and a moisture sensor developed by META. In parallel, a team of scientist and engineers at Sheffield Hallam University (SHU) conducted initial investigations in laboratory and identified the optimum process parameters. The initial findings have been cross verified with integrated MCure prototype with field trials carried out at site of Heizmann. Various volumetric cube samples with different cementitious repair materials have been cured with various microwave power. The results show that microwave curing of repair materials applied under ambient temperatures has no negative effect on the repair/substrate interfacial bond strength. In significant number of cases, the bond strength of the microwave cured repair material is slightly higher than normal cured repair. Microwave curing of repair material under an ambient temperature of -5 °C provides significantly higher bond strength compared to SoA curing of all kinds of material which were carried out in the test. Background trials performed in laboratory and field trials performed at the location of end user company Heizmann has validated the technical concept and the market opportunity. The company Uvasol disseminated the results to companies involved in relevant sector and coordinated with RTDs to published selected non-confidential results. It is expected that within five post project years, MCure will generate new jobs in EU and additional revenues for the SMEPs.

Project Context and Objectives:
Over 50% of expenditure in the EU construction sector is on repair and refurbishment of existing structures rather than on new build. This has generated a requirement for industry to deliver more durable and effective repairs to concrete structures. Within the current economic outlook, with public and commercial expenditures under pressure, it is anticipated that the proportion spent on repair will rise but at the same time, the demands to ensure that the repairs are of sufficient quality, durability and cost effectiveness will also increase.

Accelerated concrete curing is especially useful when repair takes place in cold weather. Existing accelerated curing technologies like temporary heated enclosures are very expensive and the heating is inefficient. The main problems of different types of heaters like open flame gas heaters are the poor control of curing due to conventional heat transfer into concrete and also safety issues. Steam curing, currently the most effective state of art technique, is not feasible for in-situ curing required for concrete repair.

A need had therefore been identified, with significant market potential, to improve the quality, control and speed of the curing process in concrete repairs. By achieving such control, the productivity of the construction sector can be significantly improved, reducing the time that resources are idle whilst curing is either being completed under ambient conditions or is not possible due to cold weather. In order to fulfil the needs of rapid curing, all weather construction activity and long term durability, the project MCure has been executed. It researched, developed and demonstrated at a prototype level, an economically viable system to reduce the curing time and improve the quality of concrete curing especially in repairs using microwave technology. To achieve dual benefits of economy, due to both high turnover and improve strength/durability, provided by the MCure accelerated curing system due to its high control of temperature, rate and duration of temperature rise in the curing medium. In contrast, the poor temperature control of SoA accelerated curing only provides the economic benefit of high turnover but with greater fuel and environmental costs and the strength/durability of the end product is inferior. This MCure technology is a step towards improvement of concrete repairs quality undertaken by EU SMEs involved in construction sector through the research and technology development of a novel accelerated microwave curing system. It will enable more efficient use of resources, especially in harsh winter weather conditions due to the system robustness and the effectiveness of the technology in all kinds of weather. This technology will increase the durability and strength of the repaired concrete.

Project Results:
Description of Technological Results

The main technological result of the project is an integrated mobile demonstration unit for concrete curing. This integrated technological result consists of mechanical, electrical, automation and microwave modules.

The mechanical module consists of the linear axis which mainly contains 3 linear motion units and 3 correspondent motors. They are termed as X, Y and Z axis. The movement of X directs from Left to right Y moves front and back and Z axis moves up and down direction. The load capacity of the linear axis system is 50kg, which is about the weight for the microwave generation and transmission system. It offers us the possibilities to move the microwave transmission system in 3 directions with distances 1500mm, 1255mm and 300mm in x, y and z axis respectively in order to cover the whole concrete block. The correspondent motors provide the 3 linear motion units as moving speed for maximal 100mm/s to minimal 1mm/s. The motor installed on vertical z-axis has a brake. The brake is used to hold the motor shaft, if the system is in static condition. In addition mechanical module includes consisting of metallic fabric, 1 security limit switch and 4 pieces of microwave leakage sensors. The semi- transparent stainless steel fabric provides us a shielding effect for ca. 55dB against electromagnetic waves

The microwave module consists of magnetron, waveguides, microwave power sensor and antennas. We have tested slotted waveguide and rectangular horn antenna for curing experiments. The power of the magnetron can be regulated in a range of 200W to 2000W through the control cabinet. The rectangular horn antenna covers area of size 330*245mm; meanwhile the slotted waveguide antenna covers area of size 90*500mm

An automation module includes a control cabinet developed according to prepared wiring plan and contains the electronic devices (e.g. Operating panels, PLC, Sensors, Switches, Relays etc...).

Description of Scientific Results:

Field trials were carried out with four commercial repair materials and Ordinary Portland Cement (OPC) concrete, cured with MCure prototype system. The results with the MCure prototype on the following aspects of microwave curing of repair have been investigated and detailed out in Deliverable report 5.1:

• Relationships between the microwave curing parameters (P, t, V) and the curing temperature rise ∆T, leading to the development of the algorithm for automatic control of the MCure prototype.
• Effect of microwave curing and state-of-the-art curing on compressive strength of repair.
• Effect of microwave exposure on compressive strength of substrate concrete.
• Effect of microwave curing on repair/substrate and repair/reinforcement bond strength.
• Non-destructive monitoring of internal temperature to determine the effect of microwave curing on temperature rise, including its effect on cement hydration.
• Effect of microwave curing on porosity and pore structure by mercury intrusion porosimetry testing.
• Pilot run on the MCure prototype to optimise operating parameters such as antenna position and microwave power range. A saturated sand slab was used in the trial.
• Pilot run of the MCure prototype moisture sensor for non-destructive monitoring of moisture.

In addition to results of the above mentioned investigations, relationship between curing parameters and their validation have been performed with the following objectives:
• Evaluate the effect of microwave curing parameters on different formulations of commercial repair materials including concrete in scaled up tests on slabs of dimensions 1 m x 1 m and depths ranging between 34-80 mm.
• Plot the relationships between temperature rise ∆T and curing time by measuring, at each time increment, the internal and surface temperatures of the repair patch with sensors, thermocouples and a thermal camera.
• Simulate a repair patch applied to a hardened concrete substrate and a repair patch with steel reinforcement in it. Monitor the ∆T versus curing time relationships.
• Validate the relationships previously developed in laboratory studies between the parameters of microwave curing, such as power, curing time, volume of repair and microwave curing temperature rise ∆T.
• Estimate the microwave energy used to cure the slabs

Microwave curing a concrete slab with two cycles provides a 32% higher temperature compared to microwave curing the slab with one cycle over a constant time period. The Microwave prototype system tests on scaled up slabs of repair materials validated the general relationships between the curing temperature ∆T and microwave curing parameters of power, time and volume, which were developed from earlier laboratory tests. This relationship applies to relatively similar chemical compositions of repair materials. Repair materials with significantly different temperature-time relationships under a constant microwave power will deviate from this relationship.

Potential Impact:
The MCure project is aimed to improve the competitiveness of the EU repair and refurbishment sector; improving the quality and speed of repair and refurbishment of concrete structures. The construction sector is a large part of Europe’s economy, even in the difficult economic times and accounts for 50% of the annual European construction budget spending. Furthermore, this sub-sector is dominated by SMEs which accounts for 72.1% of employment i.e. 14.1million people in EU27. The climatic conditions cause fluctuation in the employment number in this sector because the curing of concrete structure is challenging in certain weather conditions. The MCure offers possibilities for these SMEs to work independent of climatic conditions. Beside increment in competitiveness and quality of concrete curing, the reduced fluctuations of employment depending on climatic conditions will improve the certainty for laborers. The MCure system will assist in promoting the construction sector as a driving force in the creation of jobs especially in winter and for sustained growth of the economy in general. The construction sector in many EU member countries is inclining towards growth. In addition, the EC itself is currently promoting the construction sector as a driving force in the creation of jobs and for sustained growth for the economy in general.

The cost of repair can be substantial depending on the scale and severity of the damage. Concrete structures prone to damage can be publically, commercially or privately owned. To emphasise the importance of accelerated concrete curing during repair, an example of repair on concrete bridge can be considered. Bridges are an important transportation link in modern societies, and bridge closures for refurbishment can have major impacts on the local or wider economy. The time to repair a bridge quickly is crucial than the cost of repair itself due to user costs, traffic delays and lost productivity that have been estimated to be more than ten times the direct cost of maintenance, repair, and rehabilitation. User costs are estimated as the product of additional travel time, impact on environment by burning extra fuel and the value of time. It is therefore essential to accelerate the repair because of the additional cost being spent on upgrading of the detour highways. These detours impact on both social and commercial travel, impeding worker’s commercial activity whilst they are delayed in traffic.
This proposed technology is aimed to cure all kinds of concrete structures. If just one market segment alone is considered; the repair and refurbishment of bridges, targeting this one sector will create a lot of opportunities for SMEs to expand their business not only in EU but also worldwide. The technology has been validated at pre industrial scale during this project and SME consortium members of the project are aiming to further continue the work for industrial scale validations. Once the technology has validated at industrial scale in EU it can then be used to fuel export sales, generating revenue and creating jobs in Europe. There will be huge potential to export this technology across the world, for example there are 583,000 bridges in the United States (1998) and 235,000 of this total are conventional reinforced concrete including 108,000 bridges constructed of pre-stressed concrete. Approximately 15% of the bridges are structurally deficient and need repair. The annual direct cost of repair for structurally deficient bridges over the next ten years is €1.56 billion (Bn) for maintenance of concrete bridge decks and €1.56 Bn for maintenance of concrete substructures (minus decks). Life-cycle analysis estimates indirect costs to the user due to traffic delays and lost productivity at more than ten times the direct cost of corrosion maintenance, repair, and rehabilitation.

The dissemination activities especially through MCure video have attracted lot of attention from possible end users. The dissemination manager of MCure project has been contacted by few companies in UK, who have curing issues to work in winter. They are looking forward to test this technology. SMEs led by dissemination manager have organized the post project dissemination activities and will display technology in Sheffield to concrete repair association and all the interested companies. The dissemination of results has also raised queries for application of MCure technology in the precast concrete items and slipform constructions. Based on interest shown by end users, consortium is aiming to mature the technology at industrial scale for sales in market. The development of this technology will not only impact jobs in construction sector but also in technology sector for development of MCure machines.

List of Websites:

Project Coordinator
Siegfried Egner
Phone: +49 711 970-3643
Technical Manager
Ali Imran Javaid
Phone +49 711 970-3628