ABSTRACTThis paper presents a complete methodology that allows selecting optimized solutions for the extension of service-life of concrete structures exposed to aggressive environments. The methodology combines the use of field data and advanced modeling in a comprehensive approach. The first step of the method consists in collecting data on the concrete structures using a combination of techniques such as half- cell potential and linear polarization. The field activities also include extracting cores from selected concrete elements. Specimens from cores are tested to measure the physical and chemical properties of the material. The data generated from these previous steps are used as input parameters in an advanced mechanistic chloride transport model to predict future performances of the structure. Depending on the results, different remediation scenarios can be modeled such as concrete repairs, sealer applications, and cathodic protection, and compared to the simulations where no actions are taken. The cost of each remediation scenario can be compared to its benefit, which allows identification of optimized solutions. The paper provides a detailed description of each step. Case studies are then presented to illustrate the use of the methodology for different concrete structural elements.INTRODUCTIONThe rapid deterioration of concrete structures at this time, combined at a time public funds dedicated to remediation and new construction is scarce. This unfortunate combination of events means that optimization of resources is key when planning repair of existing structures to extend the service-life expectancy of structural elements.Chloride played a significant part in the global deterioration of concrete structures. The well- documented impact of the aggressive chemical species on steel reinforcement has been the topic of numerous scientific papers and reports. This has led to the development of many chloride ingress models, whose objective is to predict the time it will take for sufficient chloride concentrations to reach the level of the reinforcing steel. However, the models are, in many cases, difficult to integrate into an engineering approach to durability. Consequently, engineers are left without proper tools to actually predict the time of occurrence and extent of damage to a structure. This in turn makes it difficult to select the most appropriate remediation solution.
Leonovich, Sergei N. (Far Eastern Federal University) | Shalyi, Eugeny E. (Far Eastern Federal University) | Falaleeva, Nadezhda A. (Far Eastern Federal University) | Kim, Lev V. (Far Eastern Federal University)
Concrete is used as the basic construction material in more than 80% of ice-resistant offshore structures. Concrete design should be characterized by an adequate durability because of the aggressive influence of external chemical and physical factors, in particular CO2. Carbon dioxide associates with the dissolved calcium hydroxide, neutralizes it and causes a loss of mass of the concrete surface layer whilst enhancing degradation. A degradation model for environmental conditions of Sakhalin offshore is presented. The main function proposed was to take into account the influence of climatic parameters in the form of a random process of rain and wind. Statistics were obtained from weather stations data at different zones of the Sakhalin island, which allowed to model the depth of concrete carbonation. Calibration was done including the variability of the material properties and environment features. Probabilistic analysis of the carbonation rate for offshore concrete structures was conducted. Results can be used in practice to estimate the durability of offshore concrete structures.
Russia has an offshore area of about 4.2 mln. Km2 but around 80% of the petroleum deposits are located in cold regions. The development of offshore oil projects needs complex infrastructure construction. 80% of the offshore structures are made of concrete which must comply with minimum durability requirements. Knowing the parameters of different degradation processes and the factors influencing them, allows to estimate the service life of reinforced concrete structures.
One of the main degradation processes along with the chloride ingress is carbonation (Leonovich, 2012). In this, the nature of the mechanism is a stochastic process that goes along with large uncertainties on the ingress of aggressive agents in combination with uncertainties on the surface properties of reinforced concrete.
Professor Moskvin (1952) has proposed three kinds of corrosion mechanisms: 1) dissolution of cement components during water filtration through concrete; 2) chemical interactions; and 3) accumulation and crystallization of reaction products causing tensile damage in a porous structure. This paper presents the results of a carbonation assessment under Sakhalin offshore conditions.
This NACE International test method has been prepared to provide users and manufacturers of embeddable anodes with a test method for evaluating the anode material to an expected lifetime criterion. It is applicable to embeddable anode materials, such as titanium (Ti) mesh, commonly used for cathodic protection (CP) of atmospherically exposed steel-reinforced concrete.
This test method presents two methods for evaluating the anode material; Test Method Part A is intended to evaluate whether an embeddable anode material complies with minimum required specifications of design life expectancy at rated current output. Test Method Part B is a quicker test to ensure that a sample from a particular batch of material is suitable. Test Method Part B shall only be conducted on samples of a product that has passed Test Method Part A for the required design life. The test methods are not applicable to surface-mounted anodes or conductive coating materials.
The test method was originally prepared in 1994 by Task Group (TG) T-3K-6, “Test Procedure for Anodes Used in Concrete,” a component of Unit Committee T-3K, “Corrosion and Other Deterioration Phenomena Associated with Concrete.” It was reviewed by TG 045, “Anodes Test Procedures” and reaffirmed in 2001 by Specific Technology Group (STG) 01, “Concrete and Rebar.” It was revised by TG 045 in 2007 and in 2015 by TG 472 (new designation). TG 472 is administered by STG 01, “Reinforced Concrete”; and sponsored by STG 05, “Cathodic/Anodic Protection.” This standard is issued by NACE under the auspices of STG 01.
Section 1: General
1.1 Accelerated testing of anodes for use in concrete is intended to provide an indication of an anode’s ability to perform satisfactorily for a specific number of years. Unfortunately, accelerated life testing cannot be conducted in concrete because testing at high-current levels results in premature failure of the concrete as the test electrolyte. Accelerated life testing must therefore be conducted in an aqueous solution.
1.2 Test Method Part A is designed to evaluate the anode material to an expected lifetime criterion, and is conducted over a period of at least 180 days. (See Section 3.)
1.3 Test Method Part B uses accelerated life testing to verify that anodes comprised of a Ti substrate, to which a mixed metal oxide (MMO) catalytic coating has been applied, meet minimum service-life requirements in accordance with the expected design life. The test is operated at higher current densities than the application’s design to accelerate the time to failure. (See Section 8.)
1.3.1 The minimum test period is 65 hours for anodes with an expected design life of 100 years at a maximum current density of 108 mA/m2 (10 mA/ft2).
1.3.2 The minimum test period is 78 hours for anodes with an expected design life of 120 years at a maximum current density of 108 mA/m2 (10 mA/ft2).
The bigger mine waste dumps create the greater the issue to encounter in situ ground conditions. Landfill rock waste makes an inadequate strength and economic issue of the reclamation work is more difficult, especially in determination of slope stability. A clear differentiation based on the lump-size rock type and soil distribution and compression in the field of reclamation. GEO5 FEM, Rocklab and Stereonet7 programs performed with four rockfill modeling and stability analysis for A1, A2, A3 and A4 rock fills models where rock fills of the dump slope were limited. Anisotropic rockfill and soil mixture models were made in laboratory scale. Heterogeneous geotechnical parameters were analyzed. Regarding the topographic maps produced in the 1/1000 scale with field work and the structural cross sections of rock fill models conducted on laboratory experiments, the physical and mechanical properties for each A1, A2, A3 and A4 Models. A1, A2 slopes were close to stable state that showed to be slight safety risk. However, GEO5 programs with limestone fill model through FEM program exhibited stability with A3 and A4.
Because of growing urbanization, reclamation of mine waste dumps is required and has to be concerned. New and bigger urbanization area may face to the reclamation issue around the civil structures. The geotechnical parameters of ground are the decisive factor regarding the type of slope stability work and its efficiency (Bieniawski 1967, Cernica 1995, Das 1994).
In the stable ground, the slope has to be actively supported in order to avoid ground settlement. Modified impact resistance of rocks makes use of the 20-30 cm lump massive rock model to provide face scale to 2-3 cm. The indentation by the drilling bit enters in-situ the massive lump rock, where the volume of rock retained can regulate through the advance rate. Depending on the resistivity of the rock volume in the dump, the indentation pressure can be controlled. The pressure can be calculated depending on the slope (bit diameter, overburden depth), geological and hydrogeological conditions and any surcharge in the area affecting the stability alignment (Görög & Török 2006, Görög & Török 2007).
The calculation of slope stability of mixed face conditions of the varied rockfills such as local porous limestone, marly limestone. The waste shale and marly shale is based on the assumption of a linear (hydrostatic) distribution of support pressure over the face, which is in equilibrium with the scaling ground and water pressures in laboratory model (Bishop 1955, Hoek 1970, Hoek 2013, Hoek & Brad 1977). However, evaluation of data is made by GEO5 FEM model program (Anonymous 2009, Anonymous 2009, Pruska 2009). Earth face in-situ measurement systems have demonstrated dynamic non-linear stress distribution with strong fluctuations at times of high tonnage lorries transfer. This showed in particular differences between the phones at the slope face and critical weakness spaces in the dumps.
Falaleeva, Nadezhda A. (Far Eastern Federal University) | Tyitrin, Roman S. (Far Eastern Federal University) | Kim, Lev V. (Far Eastern Federal University) | Seliverstov, Vladimir I. (Far Eastern Federal University)
The Russian Far East is one of the regions with severe climatic conditions, thus the structures must have the high strength and corrosive resistance. The paper presents the experimental results of concrete without clinker alkaline binders of volcanic rocks. The storage of this rocks is big on the Pacific coast of Russia. The corrosion resistance of alkaline concrete in comparison with the control on cement concrete hardening after six months in different environments (fresh water, sea water, sulfate solution, atmospheric conditions, normal hardening, freezing-thawing, wetting-drying) have proved the advantages of alkaline concrete over concrete on portland cement.
In the mining industry time is critical as production depends on the speed of the mining cycle. During the mining process, the time required to re-open access for the next phase of an underground heading is a key point that strongly depends on the ability of the selected ground support technique to promptly ensure the safety of workers. Fiber reinforced dry-mix shotcrete has been proven to be an efficient and well adapted technique, able to produce a ground support material with the required energy absorption or flexural toughness in a single application phase. In this context, this paper demonstrates the possibility of significantly speeding up the mining process by using a new fiber reinforced dry-mix shotcrete. The new fiber reinforced dry-mix shotcrete is capable of developing flexural toughness in only 24 hours that is equivalent to what is typically achieved after 28 days using current fiber reinforced drymix shotcrete technology.
Shotcrete is often used for ground support when using the drill and blast method or other tunnelling methods. But before re-opening access for the next phase of the underground heading, the applied shotcrete is required to reach a minimum compressive strength and in case of fiber reinforced shotcrete, a minimum flexural toughness (energy absorption) in order to ensure the safety of the workers going into the heading. Combined with bolts, the use of conventional fiber reinforced shotcrete becomes an interesting method for ground support as it is applied very soon after excavation and works to stabilize ground movements (Bernard E. S., 2009). In this case, the toughness development of fiber reinforced shotcrete becomes an important feature of the material when looking to speedup the mining cycle. However, early re-entry criteria in underground openings are difficult to ascertain as the load carrying capacity of fiber reinforced shotcrete is usually assessed after 7 or 28 days. For this reason, re-entry criteria varies from one mining area to another and are usually based on compressive strength requirements. For example, in northern Ontario, Canada, one of the current practices in the mining industry consists of allowing safe re-entry once fiber reinforced shotcrete has developed a compressive strength of higher than 4 MPa (Dufour, O’Donnell, & Ballou, 2003). Flexural toughness requirements on fiber reinforced shotcrete are also typically based on evaluation after 28 days.
In order to speed up the mining and tunnelling process, King Packaged Materials Company, Burlington, ON, Canada, a specialized company in pre-packaged, pre-blended dry cementitious material, has conducted a testing program to develop a fiber reinforced shotcrete mix that reaches the compressive strength and the flexural toughness required as fast as possible.
ABSTRACT: Micro fissure grouting is often applied to improve the quality of the surrounding rockmass in underground engineering. While it usually does not work in field because the cement is difficult to be injected into the rock fissure and the cement particles cannot consolidate quickly, therefore it cannot effectively strengthen the rockmass. A new grouting method DGT (Derive Grouting Technology) was presented in this paper to solve these problems. In this method, special cement with high flowability and strength in early age was developed and used as grouting material, and expelling holes were drilled around the grouting hole according to the fissures distribution to derive water out of the micro fissure and leave the cement particles inside. By controlling certain grouting pressure, the cement particles in the micro fissure accumulated and solidified quickly and the quality of rockmass could be improved in a short time, which was very important for deformation controlling of the surrounding rockmass in excavation process. In addition, acoustic testing proved the validity of the technology in an underground project.
Grouting is also called injection grout (Kuang, 2001), which is used for enhancing the impermeability and anti-seismicity of the grouting area. The purpose of the grouting with pressure is to fill the joints, discontinuities, void distance and cavities in the rock masses to consolidate and caulk the rock masses for reducing seepage and uplift pressure in dam foundation and related structures (Zadhesh 2014). By applying an appropriate pressure, grouting material which is of flowability in early age and adhesion before solidification was injected into the necessary position, thus the stability and safety of the structure could be improved. The grouting area are mainly soil mass and rock mass (Hao 2001 ). Grouting materials often include dissolvable materials and suspended materials. Dissolvable materials are mainly made up of chemical materials while suspended materials are mainly cement materials. Grouting projects often use clay, pozzolans and calces as grouting materials formerly. When Portland cement appeared in 1826, cement materials were widely used in projects (Wang 2000). When admixtures like clay, bentonite, water glass, fly ash and pozzolans were added in the Portland cement, some characters were improved (Luo 2006). By now cement grouting is usually used as one of the most important techniques for soil and rock stabilization structures (Camberfort 1967).
Kusuma, G. J. (Institut Teknologi Bandung) | Shimada, H. (Kyushu University) | Gautama, R. S. (Institut Teknologi Bandung) | Matsui, K. (Kyushu University) | Saputra, C. H. (Geology Department of PT. Kaltim Prima Coal)
Utilizing the fly ash (FA) for environmental applications, such as for hazardous waste barrier materials, is one of the common alternative of FA utilization due to its several advantages, both on the chemical and the geotechnical view. However, the FA has a range variety of characteristics and tend to be site specific which depends 0on the coal source quality and the coal burning condition. Hence, an evaluation of the geotechnical properties of FA is needed to be conducted prior to its utilization in a specific application such as an additional mixture material in a barrier material to encapsulate the sulfide containing rock in an overburden dump, in which the stability and the integrity of the dump are the main issues that have to be maintained from a geotechnical point of view. The objectives of this research are to (i) characterize the engineering properties of FA and two types of overburden rock as well as its several mixture compositions; (ii) evaluate the properties of the FA-overburden mixtures as a barrier material candidate; and (iii) determine the most appropriate composition of material mixtures that provides a high degree of confidence in achieving an acceptable design criterion as a barrier layer. In order to address these objectives, several laboratory tests such as the consistency limit test, compaction test, and hydraulic conductivity test have been done on several compositions of FA-overburden rock mixture as well as the oxygen diffusion potency. The study concludes; is was that the 10 % w/w content of the FA in the material mixture is the maximum FA addition to achieve the recommended properties of the material mixture for an encapsulation purpose of the sulfide-containing overburden rock.
To reduce the chloride permeability of concrete in practice, kaolinite clay was introduced into concrete. The effects of kaolinite clay on the corrosion process of rebar embedded in the concrete were investigated. The cylinder concrete specimens with the dimension of Ø100×50mm were prepared. All blended concrete samples were prepared using a water-to-cement (w/c) mass ratio of 0.5. Ordinary Portland cement was partially replaced by kaolinite clay at 0%, 1wt%, 3wt% and 5wt% by weight of cement. After being cured in the standard curing condition for 28 days, the prepared concrete samples were immersed in the NaCl solution, and a designed electrochemical accelerated penetration system was used to accelerate the corrosion process as well. A continuous constant current of 100 mA was applied. The corrosion conditions of the rebar embedded in the concrete were measured regularly by the nondestructive testing (NDT) method. The developments of corrosion states of the rebar embedded in the concrete samples with four nanoclay addition dosages were observed. The test results showed that the damage of rebar embedded in the concrete specimen with 5% naoclay was less than the others. It can be concluded that the nanoclay can delay the chloride penetrate into the concrete obviously. Consequently, the corrosion of the rebar embedded in the concrete is impeded efficiently.