12. Determination of chloride content in concrete structures with laser-induced breakdown spectroscopy

G. Wilsch *, F. Weritz, D. Schaurich, H. Wiggenhauser

An important criterion for the evaluation of reinforced concrete structures is the measurement of the chloride content. This will normally be done by time consuming standard chemical methods. We propose the application of a spectroscopic technique, the laser-induced breakdown spectroscopy (LIBS), which provides the advantages of a fast measurement, the potential for on-site application and the possibility to investigate a wide range of different measuring points. The surface can be scanned, or depth profiles are available from cores. Measurements can be performed directly on the sample surface and the results are available in near real time. We present LIBS results measured on concrete cores as well as on grinded and pressed material in comparison with the results of standard chemical methods. The optimum LIBS set-up and the experimental conditions to detect and measure chlorine in building materials are reported. The limits of detection were determined and calibration curves were measured. 

11. Laser Radiation CO2 Effects in Cement Paste at Different Hydration Stages after Preparation

Moreno–Virgen M.R.1, Soto–Bernal J.J.2, Ortiz–Lozano J.A.3, Frausto–Reyes C.4, Bonilla–Petriciolet A.5, González–Mota R.6, Rosales–Candelas I.7 and Pineda–Piñón J.8

1 CICATA. Querétaro, Qro. México Instituto Tecnológico de Aguascalientes. E–mail: moreno_virgen@yahoo.com.mx

2 Instituto Tecnológico de Aguascalientes. E–mail: j2sb@cio.mx

3 Universidad Autónoma de Aguascalientes. E–mail: aortiz@correo.uaa.mx

4 CIO, Unidad Aguascalientes. E–mail: cfraus@cio.mx

5 Instituto Tecnológico de Aguascalientes. E–mail: petriciolet@hotmail.com

6 Instituto Tecnológico de Aguascalientes. E–mail: Rgmota73@yahoo.com.mx

7 Instituto Tecnológico de Aguascalientes. E–mail: ilianaroca@yahoo.com

8 CICATA. Querétaro, Qro. México. E–mail: arqjpp@yahoo.com

In this work the changes occurring in cement pastes irradiated by 10.6¡mi CO2 laser at different stages of hydration after preparation are presented. Raman spectroscopy, X–ray diffraction and Scanning Electronic Microscopy (SEM) techniques were used to observe molecular structural changes. Intensity of cement paste Raman peaks after laser irradiation was monitored in samples irradiated 2, 3, 4, 5, 6, 7, 8, 9,10 and 11 days after their preparation. Applied laser power changed Raman peaks intensity at 187.5cm–1,563cm–1, 695cm–1, 750cm–1, 897cm–1,1042cm–1 and 1159cm–1 that correspond to compounds already present in cement pastes. X–ray diffraction, SEM images and changes in the Raman peaks confirm the recrystalization of cement paste compounds into new phases (alite and belite) after irradiation. The produced changes show a clear dependence on the applied laser power density and age of samples. 

10.The effect of ageing and drying on laser scabbling of concrete

B. Peach (a), M. Petkovski (a), J. Blackburn (b), D.L. Engelberg(c)

a.Department of Civil and Structural Engineering, Sir Frederick Mappin Building, Mappin Street,,University of Sheffield, Sheffield S1 3JD, UK

b. TWI Ltd, Granta Park, Great Abington, Cambridge CB21 6AL, UK

c. Research Centre for Radwaste & Decommissioning, School of Materials, The University of Manchester, Manchester M13 9PL, UK

Laser scabbling of concrete is a process by which the surface layer of concrete is removed through the use of a high power (low power density) laser beam. In order to understand how the age and treatment of structures may affect the laser scabbling process, the aim of the research presented in this paper was to establish a relationship between laser interaction time, surface temperature and volume removal for cementitious materials of different ages and different degrees of saturation. The investigation focussed on (i) the effect of age on saturated specimens and (ii) the effect of prolonged drying. The results show that drying of specimens had the largest effect on scabbling. The effect of age on saturated specimens was small for PFA + OPC pastes, mortars and concretes, but significant for OPC pastes, where the volume of scabbling dramatically reduced with age. 

9. Laser scabbling of mortars

B. Peach (a), M. Petkovski (a), J. Blackburn (b), D.L. Engelberg(c)

a.Department of Civil and Structural Engineering, Sir Frederick Mappin Building, Mappin Street,,University of Sheffield, Sheffield S1 3JD, UK

b. TWI Ltd, Granta Park, Great Abington, Cambridge CB21 6AL, UK

c. Research Centre for Radwaste & Decommissioning, School of Materials, The University of Manchester, Manchester M13 9PL, UK

Laser scabbling of concrete is the process by which the surface layer of concrete may be removed through the use of a low power density laser beam. Previous research has suggested that the driving force responsible for laser scabbling is developed within the mortar. The aim of this investigation was to establish the key parameters that influence laser scabbling of mortars. The results show that the removal of free water from mortars prohibits scabbling, but resaturation allows mortar to scabble. A reduced permeability, either due to a reduction in the water/binder ratio or the use of 25% PFA replacement, enhances the scabbling. A higher fine aggregate content increases volume removal and fragment sizes during laser scabbling. 

8. The effect of concrete composition on laser scabbling

B. Peach (a), M. Petkovski (a), J. Blackburn (b), D.L. Engelberg(c)

a.Department of Civil and Structural Engineering, Sir Frederick Mappin Building, Mappin Street,,University of Sheffield, Sheffield S1 3JD, UK

b. TWI Ltd, Granta Park, Great Abington, Cambridge CB21 6AL, UK

c. Research Centre for Radwaste & Decommissioning, School of Materials, The University of Manchester, Manchester M13 9PL, UK

Laser concrete scabbling is the process by which the surface layer of concrete may be removed through the use of a low power density laser beam. The main aim of this investigation was to establish relationships between laser interaction time and volume removal for a wide range of material compositions, including different w/b ratios, binder compositions (OPC/PFA), aggregate/binder ratios and coarse aggregate sizes. The results show that 25% replacement of ordinary Portland cement with pulverised fuel ash and/or a reduced water/binder ratio improves the efficiency of scabbling of cement pastes. Mortars and cement pastes were seen to scabble at a constant rate, whereas concretes experienced a peak rate, after which volume removal reduced dramatically. Basalt aggregate concrete was less susceptible to laser scabbling than limestone aggregate concrete. The effects of composition on the mechanisms which drive laser scabbling are discussed. It is suggested that pore pressure spalling governs behaviour in cement pastes, and thermal stress spalling is more dominant in mortar specimens. The driving force responsible for laser scabbling of concretes is developed within the mortar. 

7. Using a High-Power Fibre Laser to Cut Concrete

Kaori Nagai, Kazuki Shimizu

Department of Architecture and Architectural Engineering, College of Industrial Technology, Nihon University, Chiba 275-8575, Japan 

Concrete cutting at construction sites causes problems such as noise, vibration, and dust. In particular, during the demolition and renovation work on buildings in urban areas, protection against noise, vibration, dust, etc., is needed. Concrete cutting using a CO2 laser was investigated 20 years ago. However, this method had never used because the equipment is difficult to carry. In this study, we used a portable fibre laser, which is convenient to carry. Two types of concretes with different strengths were prepared for the experiment. High-strength concrete has never been used in similar research before. High-strength concrete is just only used for skyscrapers because of its high quality and costs. Furthermore, it has already been used for skyscrapers in Japan. It is for this reason that we chose to use it in this study. Irradiation measurements were conducted under various conditions using laser powers of 6 and 9 kW. It was confirmed that the cutting effectiveness of CO2 and fibre lasers was approximately identical for concretes with a thickness of 200 mm. Furthermore, the cutting effectiveness for the two concretes with different densities was almost the same. However, the situation after cutting was different because the vitrification of the cutting and glass formation progressed in low-density concrete and an explosion phenomenon occurred in high-density concrete, simultaneously. This study suggests that laser concrete cutting can be used as a solution when noise and dust are major problems. 

6. A laboratory study about laser perforation of concrete for application in oil and gas wells

Hasan  Kariminezhad  , Hossein Amani b, Mobarakeh Moosapoor a

a  Department of Physics, Babol University of Technology, Babol, Iran 

b Faculty of Chemical Engineering, Babol University of Technology, Babol, Iran 

Laser perforation is the application of light to make a flow path between wellbore regions through the casing wall and cement layer all the way to reservoir production zone. Due to significant losses of laser power at long distances, introducing a novel method in order to facilitate laser perforation in oil and gas reservoirs is necessary. This paper aims to study on concrete perforation using a continuous 240 W/cm2 CO2 laser. In this research, the effect of water on the parameters of laser perforation such as rate of perforation (ROP), specific energy (SE) and dominant mechanisms was investigated. For this, two groups of concrete samples (dry and wet) were illuminated at 2, 6, 15, 30 and 60 s by the laser. Our results showed evaporation was main mechanism for dry samples at exposure times above 15 s, while spallation was the dominant mechanism for the wet samples at all exposure times. ROP and SE were significantly increased and decreased in the presence of moisture, respectively. Maximum ROPs obtained 2.26 mm/s and 0.45 mm/s for wet and dry samples, respectively. Also, minimum of SEs for wet and dry samples obtained 1.05 J/mm3 and 4.3 J/mm3, respectively. Finally, our experimental results were justified using a simplified heat conduction model. All these characteristics demonstrate presence of water in concrete possesses an important role to improve rate of laser perforation. Therefore, the results of this research could significantly reduce time and cost of laser perforation for application of oil recovery. 

5. Development of Concrete Building Cutting Technology Using High-Power Laser

Goya, S., Mori, H., Okuda, T., Fujiya, Y., Shimonabe, N., & Akaba, T. 

With the increasing power and better quality of laser oscillators, laser processing, which has not been applied to thick concrete, has been increasingly used in recent years. In this report, we describe laser cutting of thick concrete columns (with a maximum thickness of 1200 mm) by using high-power fiber laser of over 20 kW and an ultra-long focus optical system, aiming at establishing a remote demolition technology for nuclear plant buildings that are high radiation areas. This report also describes a new beam laser damper system using water that was developed as a technology for receiving the high-power laser beam passing through a cutting object, which has been an issue in high-power laser processing. 

4.  An experimental investigation of laser scabbling of concrete

B. Peach*, M. Petkovski*, J. Blackburn**, D.L. Engelberg***

*Department of Civil and Structural Engineering, Sir Frederick Mappin Building, Mappin Street, University of Sheffield, Sheffield S1 3JD, UK

**TWI Ltd, Granta Park, Great Abington, Cambridge CB21 6AL, UK

***Research Centre for Radwaste & Decommissioning, School of Materials, The University of Manchester, Manchester M13 9PL, 

UK

Concrete is widely used in the nuclear industry, often in direct contact with radioactive materials.

Concrete contamination tends to extend 8–12 mm from the surface

Mechanical scabbling has flaws, but lasers have the advantage of being remote.

Laser scabbling and surface glazing, with subsequent surface removal, was used successfully in the decommissioning of the Japan Atomic Energy Research Reprocessing Test Facility

Laser scabbling is comparable to explosive spalling exhibited in concrete exposed to fire conditions, but the large difference in heating rates would be expected to produce different mechanisms driving the two processes.

The aim of this research was to establish an experimental methodology for detecting the mechanisms responsible for laser scabbling of concrete.

The results of this study show that the scabbling behaviour of each material can be characterized by time histories of average surface temperature of the exposed area of the specimens.

The results show that the laser scabbling process is significantly affected by the material composition, with clear differences between cement pastes with different binder mixes; between cement pastes, mortars and concretes; and between concretes with the two different types of aggregates used in this study.

The results of this study showed that the size of fragments was generally smaller, and vitrification was more prominent, for saturated specimens compared to air dried specimens, but the higher degree of saturation did not lead to increased volume removal. This indicates that the presence of free water does affect the process, but is not a key factor controlling its effectiveness.

3.   Performance comparison of CO2 and diode lasers for deep-section concrete cutting

Philip L. Crouse , Lin Li *, Julian T. Spencer a a, b 

a . Sackville Street, Manchester M60 1QD, UK 

b. BNFL, R&T, Rutherford House, Risley, Warrington, WA3 6AS, UK 

Layer-by-layer laser machining with mechanical removal of vitrified dross between passes is a new technique with a demonstrated capability for deep-section cutting, not only of concrete, but of ceramic and refractory materials in general. For this application fairly low power densities are required. A comparison of experimental results using high-power CO2 and diode lasers under roughly equivalent experimental conditions, cutting to depths of >100 mm, is presented. A marked improvement in cutting depth per pass is observed for the case of the diode laser. The increased cutting rate is rationalized in terms of the combined effects of coupling efficiency and beam shape.

2. Effect of moisture content and mix proportion of concrete on efficiency of laser scabbling 

Seong-Uk Heo a , Ji-Hyun Kim b , Seong Yong Oh c , Gwon Lim c , Sungmo Nam c , TaekSoo Kim c , Hyunmin Park c , Chul-Woo Chung a,* 

a . Division of Architectural and Fire Protection Engineering, Pukyong National University, Yongso-ro 45, Nam-gu, Busan 48513, Republic of Korea 

b. Multidisciplinary Infra-Technology Research Laboratory, Pukyong National University, Yongso-ro 45, Nam-gu, Busan 48513, Republic of Korea 

c. Laser Application Research Team, Korea Atomic Energy Research Institute, Daedeok-daero 989beon-gil 111, Yuseong-gu, Daejeon 34057, Republic of Korea 

With the decision to permanently shut down Kori Unit 1, the importance of domestic nuclear power plant decommissioning technology has been strengthened, and the size of the domestic decommissioning market is expected to grow to about $7 billion by 2080. Concrete accounts for more than 70% of nuclear power plant facilities as a major construction material. Therefore, removing contaminated concrete is key to reducing the cost of decommissioning nuclear power plants. There are various removal methods, but all of them have disadvantages, and a method that came out to compensate for this is laser scalable. In this study, the effects on the moisture content and mixing ratio of concrete during laser scapular were investigated.

The mixing ratio of the concrete used in the experiment is shown in Table 2.

The specimens were divided into three conditions: OD (Oven dry), AD (Air dry), and SSD (Saturated surface dry).

Each specimen was prepared as follows. First, after concrete is poured, it is cured for 1 day. After that, it is left in a saturated lime solution for the remaining 27 days until the compressive strength test on the 28th.

after

OD: dried in an oven at 105°C for 60 hours

AD: It dried for 7 days at room temperature.

SSD: Only the surface water was removed with a dry towel.

The experimental results according to moisture are shown in Table 3.

The experimental results according to the composition are shown in Table 4.

Fig. 4 shows thermal images during the scheduling process in AD and SSD states.

Fig. 5 is a thermal image during the scaffolding process in the OD state.

The phenomenon of temperature drop in Figure 4 is caused by spalling, and as a result, as shown in Table 4, OD and SSD have better scheduling efficiency than AD. The phenomenon of temperature drop in Figure 4 is caused by spalling, and as a result, as shown in Table 3, OD and SSD have better scheduling efficiency than AD. The change in efficiency according to the composition was not large as shown in Table 4.