Proceedings of the Creative Construction e-Conference (2022) 009 Edited by: Miroslaw J. Skibniewski & Miklos Hajdu https://doi.org/10.3311/CCC2022-009
Characterization of Concrete Exposed to Marine Environment
Dora Kolman, Petra Štefanec
1, Anita Radoš
2, Šime Pulić
2, Ivan Gabrijel
11 University of Zagreb, Faculty of Civil Engineering, Zagreb, Croatia, dora.kolman@grad.unizg.hr;
petra.stefanec@grad.unizg.hr, ivan.gabrijel@grad.unizg.hr
2 TPA Quality Assurance and Innovation Ltd., Dugopolje, Croatia, sime.pulic@tpaqi.com;
anita.rados@strabag.com
Abstract
Concrete can be found in various types of environments during its service life. Marine environment is one of the most aggressive and complex due to its diverse actions and variable nature. Achieving designed service life with the least embodied energy for materials production, construction and maintenance of marine structures is an important task. To meet the criteria of economy and environmental protection, concrete is made of locally available cements and aggregates. Additional benefits to reduce energy consumption but also to prevent landfills can be achieved if part of the cement is replaced with by−products of other industries. A research project entitled ‘’Concrete development for sustainable construction in the marine environment’’ aims to develop an optimized concrete mixes for Adriatic marine environment. This paper gives the overview of activities planned to achieve that goal. The project focuses on the design of the composition of the concrete mix, striving for an optimally sustainable solution between service life, energy consumption and environmental impact.
© 2022 The Authors. Published by Diamond Congress Ltd.
Peer-review under responsibility of the scientific committee of the Creative Construction Conference 2022.
Keywords: concrete characterization, marine environment, optimization, sustainable construction.
1. Introduction
Concrete can be found in various types of environments during its service life, and one of the most aggressive and complex is the marine environment. The mechanisms of degradation in such an environment are numerous, and the most pronounced is the corrosion of reinforcement caused by the action of chlorides. The intensity and interaction of degradation mechanisms depend on the local specifics of each region - (micro) climatic and weather conditions, chemical composition of water, presence of local pollutants from industrial plants or seaports, changes and flow rates, use of maritime structures, etc.
Typical salt content in seawater is about 3.5% (salinity of the Adriatic Sea is approximately 3.8%), and the majority are NaCl and MgSO4. Sea water also contains dissolved gases (O2, CO2, H2S) and numerous living organisms (mollusks, shellfish). Seawater temperature varies from -2°C (freezing point) in colder regions, to 30°C in tropical areas [1]. In warmer water, degradation of concrete is the result of chemical action, i.e., changes in the composition of cement caused by chlorides and sulfates. In colder water, the chemical action is less pronounced, and the main damage is caused by temperature fluctuations between water and air, which affect the moisture content and growth of marine organisms [2]. Concrete is exposed to cycles of wetting and drying, heating, and cooling, and freezing and thawing (colder climates) during high tide and low tide. Dissolved salts penetrate deeper and deeper into the pores of the concrete during the wetting and drying cycle. Winds, storms, and earthquakes can create high power waves. Structures exposed to waves show concrete degradation caused by erosion, abrasion, and cavitation, which manifests as surface
wear of the material. It is important to mention sea dust, i.e., seawater particles formed by breaking waves and carried by the wind over long distances [1]. Degradation of concrete in the marine environment is caused by physical and chemical influences. Physical ones occur due to pressure due to crystallization of salt which creates cracks and opens the way to chemical influences, i.e., water penetration and initiation of chemical reactions of dissolved substances with hydration products of cement or aggregate [2]. Table 1 lists the most common participants in chemical reactions between seawater and concrete and their consequences on the durability of concrete.
Concern for sustainability is constantly posing new challenges in the areas of resource management and thus in the cement and concrete industry. The desire to reduce energy consumption for the construction and production of construction materials imposes the need for the most rational use of raw materials.
Therefore, it is necessary to encourage the use of locally available materials and reduce the share of Portland cement in concrete at the expense of replacing part of the cement with by-products of industry.
The use of by-products of other industries simultaneously protects the environment because it reduces the amount of deposited material and reduces the likelihood of environmental pollution. The implementation of these activities in the construction of structures located in the marine environment is a challenge for the concrete industry. This is the theme of the project entitled ‘’Concrete development for sustainable construction in the marine environment’’ (RBOGMO) funded by the European Regional Development Fund. Research within the project is being conducted for the Adriatic coast of the Republic of Croatia. The project aims to include various parameters that are important for sustainable construction, such as local climatic specifics, identification of locally available aggregates, cements and secondary raw materials, their characterization and optimization of concrete composition. This paper presents the planned course of activities within the said project.
Table 1. Participants in chemical reactions between seawater and concrete, and their influences [2].
Reactants - seawater Reactants -
concrete Products Influence
MgSO4,CaSO4, K2SO4 C3A, CH, C-S-H
Ca6Al2(SO4)3(OH) x 26H2O, Mg(OH)2, Al(OH)3, CaSO4, SiO2 x nH2O, M-S-H
Leaching, expansion, cracking
CO2, H2CO3, Na2CO3, K2CO3
CH, Ca6Al2(SO4)3(OH)
x 26H2O CaCO3
Local softening, disintegration, leaching, corrosion (carbonation)
K2O, Na2O
Silica or carbonate constituents of the aggregates
Na2SiO3, K2SiO3
Alkali-aggregate reaction, expansion, cracking
NaCl, MgCl2 C3A, CH, Fe(OH)2 Chloraluminates,
Fe2O3 x H2O Corrosion of reinforcement
2. Research methodology
The activities envisaged by the research within the project are shown in Fig. 1. In the first phase of the project, data were collected on locally available sources of mineral admixtures that remain as a by-product of other industries, and their use in concrete is justified. In addition to mineral admixtures, data were collected on the types of cement produced within the nearby region. After the analysis of available raw materials, those materials that will be used in further research on the project will be selected, for which the possibility of contributing to the improvement of concrete properties will be assessed. Detailed characterization of selected materials by standardized and advanced test methods was performed to assess their suitability for use in concrete. In addition to the characterization of the material, a literature review was conducted aimed at investigating the interdependence of properties and composition of concrete and the resistance of concrete to actions from the marine environment. To properly select the
materials to start with designing the composition of concrete and optimization, additional data collection (sampling and their characterization) was carried out from real existing structures built in the marine environment. The research is focused on structures for which data on the properties and composition of concrete and applied construction technology are known. In the final phase of the project, the collected data will be implemented in a database that will also be the basis for computer-aided design of concrete compositions.
Fig. 1. Schematic representation of project activities.
2.1. Cement and mineral admixtures
There are two cement factories on the Adriatic coast that cover the needs of the local cement market, and in addition, there are two cement factories in neighbouring Bosnia and Herzegovina. All these cement factories produce Portland cements and certain types of metallurgical or pozzolanic cements. Reducing the amount of cement in concrete while achieving appropriate mechanical and durable properties can be achieved by replacing part of the cement with mineral admixtures. Significant amounts of fly ash from coal- fired thermal power plants have been found to be available from mineral supplements in the region. Flying ashes from several wood-fired thermal power plants are also available, and their use in concrete has been intensively investigated in recent times. In addition to fly ash, the possibility of using red sludge from a factory in Bosnia and Herzegovina will be analysed. In addition to these admixtures, the research will also include silica dust and metakaolin, which, although not locally available, play an important role in achieving better durability properties. Selected mineral admixtures have a justified application in concrete, especially those exposed to aggressive marine environment, as they improve its properties or give it special properties by various mechanisms of interaction between solid particles [3]. The use of selected mineral admixtures improves the workability of concrete by reducing the size and number of gaps between relatively large grains of cement, and releasing trapped water, which contributes to better fluidity [4]. Mineral admixtures reduce the permeability of concrete by improving the pore structure and increasing the pore density. This reduces the possibility of penetration of aggressive substances into concrete (especially chloride with a decrease in the diffusion coefficient) and the occurrence of alkaline-aggregate reaction. In addition, mineral admixtures contribute to increasing the compressive strength of concrete and its durability [3, 5, 6, 7, 8, 9].
The potentially negative contribution of mineral admixtures is reflected in the possibility of reducing the workability of concrete, which is often attributed to the increase in solid surface area due to the presence of fine particles that tend to adsorb water, replacement with filler containing large particles (> 45 µm) and open porosity of the particles which increases the specific surfaces [3, 4]. Also, mineral admixtures can have negative effects on concrete properties in the form of reduced early compressive strength which can lead
to higher permeability and lowering the pH value of concrete in favor of corrosion, so it is necessary to pay attention to composition, selection and dosage of mineral admixtures [3, 10, 11]. In general, mineral admixtures act on the principle of pozzolanic reactivity, increasing the content of C-S-H gel that binds more cement and aggregate particles to form a cohesive structure, on the principle of filling (fillers) structures reducing permeability, and on the principle of nucleation [12].
2.2. Analysis of existing structures
The project will include tests on reinforced concrete from 5 seaports along the Adriatic coast in the territory of the Republic of Croatia (Fig. 2) to cover different microclimatic conditions (seawater composition, wind intensity and frequency, etc.). The choice of structures covered by the research is limited to those for which there is extensive data on the period, conditions and construction technology, concrete composition, control test results and data on the origin of concrete components, to establish a relationship with condition and properties.
Fig. 2. Map of the Republic of Croatia showing the locations of seaports.
Pure Portland cements and Portland cements with the addition of slag or fly ash were used to produce concrete of selected structures, in quantities from minimum 340 kg (concrete element of seaport in Zadar) to maximum 430 kg (concrete element of seaport in Rijeka). Values of water-cement ratios vary from a minimum of 0.39 to a maximum of 0.45. The aggregates used are natural limestone, added in 3 different fractions: 0-4 mm (most of the total amount of aggregates), 8-16 mm, 16-32 mm. Various superplasticizers have also been added to the concrete mixes. In addition to the visual inspection and assessment of the condition of the structures, drilling of rollers was carried out for the purpose of characterizing the concrete.
For each structure, three characteristic zones are analysed:
• 1st zone - part of the structure constantly immersed in sea water
• 2nd zone - part of the structure in the part of the tides
• 3rd zone - part of the structure constantly exposed to the atmosphere (air)
Characterization of concrete samples from selected structures will be conducted to gain insight into the current state. Comparison of compressive strength and measurement of chloride diffusion of concrete installed in the structure with the properties determined by control tests during construction are
performed. In addition, to analyse porosity and chemical composition by depth, certain tests will be performed to determine the zone of influence of the marine environment.
a b
Fig. 3. (a) Degradation of concrete from analyzed marine structures caused by leaching on the surface in the splashing zone; (b) Degradation of concrete from analyzed marine structures caused by growth of shellfish in the area under the sea.
3. Optimization
The optimization process will include the preparation of test mixtures, varying the proportion of individual mineral admixtures. By optimizing the composition of concrete with selected mineral admixtures, efforts will be made to improve its durability and resistance when exposed to aggressive marine environment.
During the optimization, different approaches to the design of concrete compositions will be considered, and the possibility of making self-compacting concrete will be explored as well. At the same time, a computer program for designing the composition of concrete exposed to the marine environment will be developed. A database with the properties of locally available concrete components will be integrated into the program.
4. Conclusion
The mechanisms of degradation of concrete exposed to the marine environment are numerous, and the most pronounced is certainly the corrosion of reinforcement caused by the action of chloride. To overcome this problem, efforts will be made to increase the resistance and, consequently, the durability of concrete exposed to the marine environment. Therefore, the main aim of the project entitled ‘’Concrete development for sustainable construction in the marine environment’’ is to optimize the composition of concrete to improve its properties, and at the same time, to promote sustainable, green building. The optimization of concrete will be contributed by using locally available mineral admixtures as a replacement for part of the cement to keep its consumption as low as possible. Thus, the economic and environmental aspects gain in importance. Through the project, the aim is to develop a computer program to simplify the process of designing the composition of concrete and modelling its properties, which will ultimately make a positive contribution to optimizing the composition of concrete.
Acknowledgment
This research is supported by project entitled ‘’Concrete development for sustainable construction in the marine environment’’ (KK.01.2.1.02.0093), funded by the European Regional Development Fund.
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