Report on Sulfate concrete resistance to corrosion
Introduction
Sulfate ions are the main impediments to concrete attaining its full compressive strengths commensurate with the field requirements. It causes either softening or decays of the concrete matrix and an additional expansion due to the formation of ettringite (Panesar, 34). Sulfate attack is either internal or external based on the nature of contact between concrete and sulfate components. Sulfates tend to originate from seawaters, action of the bacteria in sewers, sulfates present in bricks as well as oxidations on the minerals adjacent to concrete surface (Bai, 1). Internal sulfate attacks occur when a sulfate source incorporates in the concrete during mixing thus becomes a component of concrete from the onset. However, external attacks occur where water with dissolved sulfates are exposed to the concrete. Therefore, any remediation plans on the sulfate attacks on concrete should be conscious of the form of concrete attack present in the field. Sulfate concrete on the other hand, is mixed and treated with cement that would reduce the corrosive activity of sulfur compounds (Slag cement association, 1). This research therefore aims at highlighting how sulfate concretes are resistant to the corrosion attacks from sulfate environments. It provides mechanisms on how both the external and internal attacks are limited by the incorporation of sulfate resistant concrete.
Purpose of the topic
Sulfate attacks remains the most significant corrosive factor impeding the efficient use of concrete in construction industry. Moreover, sulfur compounds are pervasive to most environments that civil engineering is undertaken for example, most water contain these elements. Therefore, this research identifies the effectiveness of sulfur concrete as the solution to this challenge to provide a baseline for further use and to enlist the areas for further research to develop such concrete in the field. Additionally, there is a growing interest in the use of alternative cements other that Portland cements such as the calcium aluminate and calcium sulfo-aluminate cements. Their high rapid strength attainment and setting qualities are making them useful for application in extreme environments thus informing the need for their study to scale their usability in construction.
Background research for the topic
The research aims at showing how the sulfate concretes resist corrosion focusing on the external and internal aspects of such concretes that initiates a control in corrosion. The matrix of the sulfate concrete design is such that it should limit the entry and reaction patterns of sulfate ions. The research will base on extensive literature reviews carried out from publications and previous researchers on the topic. In this regard, consolidation of the perspectives and the assertions provided by the different researchers will provide us with the calculations and the functionality of a sulfate concrete.
The application of the research is a justification of the use of sulfate concrete in the control of sulfate related corrosions. It identifies the various ways in which sulfate attacks concrete providing the appropriate sulfate concretes applicable to finding solutions to the same. This will provide a baseline with which civil engineers will decide for the relevant solutions to control of sulfate attacks based on the severity and the type of attack at hand.
Sample design calculations
Calculations involved changes in the weight of the sample, water absorption, amount of sulfate on the specimen and water content ration. Corrosion involves degradation of significant parts of concrete thus calculations will base on changes in mass for the different samples in test.
Change in strength due to exposure
CAC
These equations show the chemical reactions of sulfate attack thus informing the appropriate cement compositions in the development of concrete to safeguard against sulfate attack.
Field-testing
There were field test to ascertain the resistance of concrete to corrosion. First, there was a test on the geo-polymer concrete of heat cured low calcium based fly ash to show the capacity of resistance to sulfate attack. Here, the appropriate concrete mixture was cured in heat at 600 for 24 hours before immersing in a sodium sulfate solution of 5%. After a year of exposure, there was evaluation basing on the changes in length, mass and compressive strength. In evaluating the change in mass and compressive strengths, the test specimens were cylinders while for the change in length, the specimen was. Rangani (2009) in his test revealed that heat cured low calcium based fly ash provided an excellent resistance to sulfate attacks (Rangani, 220). The absence of cracking signs, surface erosions of sparling indicated that this component added to concrete constitutes a sulfate concrete.
The second test was the ASTM C1012 method; it aims at determining the changes in length when a mortar bar is immersed in a sulfate solution. In this method, the mortar bars are cured until attainment of a compressive strength of 20MPa after which they are immersed in a sulfate solution. The solution in use for this test will contain 352 moles of per m3. Basing on the different environmental conditions, other sulfate solutions will be relevant based on the nature of sulfate prone to the particular area of interest. The third test was a conduction of ASTM C452, the objective of this is to determine the expansion of mortar bars when Portland cements encounters sulfate components.
There will also be cube crushing strength test, this will be carried out on various concrete samples both after and before exposure to sulfate solutions. This test will show the variability in compressive strength for the various samples. This is important in that it will inform the concrete material with the highest resistance to corrosion after exposure to the sulfite conditions.
Report by California department of transportation suggests another method that is used in this study. The test differs from ASTM standard tests since the there is a maintenance of PH and concentration of sulfate at some constant while basing on the changes in strength rather than expansion as a measure for sulfate resistance (Monteiro et al, 10). This test is performed on nine cements four Portland, three calcium aluminate and two calcium sulfoaluminate. Here, 12.7 mm of hydrated concrete cubes are immersed in a solution of circulating Na2 SO4 of 4 percent and a constant PH of 7.2. The PH allows for a simulation of slight acidic conditions present in a typical field. Moreover, the specimen dimensions are sort in such a way as to maximize the surface to volume ratio to increase the surface area exposed for the permeation of sulfate ions. Moreover, the high ratio was useful in the reduction of testing time by seven weeks as the rate of sulfate permeation marked significant decrease. Identification in the variation in sulfate resistance from the various test specimens provides the appropriate cement relevant to attainment of a sulfate concrete resistant to corrosion (Monteiro et al, 6). The ultimate compressive strengths in comparison to initial provide the variations in strength based on different sulfate attack environments. The schematic diagram shows how the test is conducted.
Previous testing provided an elaborate variation in sulfate resistance for the various cements under test. Most manufacturers of the cements did not want disclosure of their cements thus the results were withheld for public view. However, it was evident that Type I, II, III and V cements had considerable sulfate resistance being that they have similar chemical compositions. Moreover, the research established that type III cements have low C3A content making it highly resistant to sulfate attacks.
Field testing in New York
States have material testing laboratories majoring on concrete soils and other materials to ascertain their suitability in the construction industry. In New York, concrete placed for any building requires tests to ensure its meets the structural design requirements. A test carried out requires a licensed expertise to preside over the field activity. Therefore, if this tests were to be in New York, people carrying out special inspection by a regional materials engineer well conversant with the procedures and the relevant codes on the suitability of such materials. Alternatively, their representatives will have to be present during the process of batching with the material available in the list of approved materials prior to their use. This is so because all concrete must conform to some mix design criteria. Additionally, tests have to conform to the NYSDOT standard specifications before they can provide an elaborate overview of the tests relevant (New York State Department of transportation materials Bureau). Additionally, there are safety concerns related to the different tests therefore important for the user to be aware of appropriate environmental, health and safety parameters to be considered when performing such tests. Therefore, the authorized personnel have the knowledge on the effective use of such tests devoid of any safety issues. For example, fresh hydraulic cementious mixtures have caustic properties and may cause burns to tissues or the skin and only authorized personnel will have the requisite knowledge on how to handle such materials.
The certifications required for the tests bases on the American Concrete Institute in New York that provides certification programs mandatory for any materials testing intervention. The first is concrete field-testing technician that will require an individual to have performed seven basic ASTM test methods and practices (American Concrete Institute). There is also concrete strength testing technician who the agency will deem as having the requisite knowledge on performance, record and testing laboratory procedures on flexural and compressive strengths of concrete. ACI highlights the four relevant ASTM practices that the technician should have knowledge about (American Concrete Institute). Third is a concrete construction special inspector, whose area of expertise should cover concrete pre-placement, placement and post placement operations. This will ensure that the inspector can oversee the appropriate testing of the different concrete components. The inspector would also ensure that the appropriate methodology and test control is performed commensurate with the environment in question.
From the tests from previous researchers show that there exist variability in resistance to sulfate attack. Testing a variety of concrete and cement properties provides a baseline for the most appropriate systems relevant to controlling sulfate attack. Thus, this research paper builds on the need by construction industry to consider alternative sources of sulfate attack in concrete that presents the major challenge.
Bibliography
Monteiro, Paulo et al. Ccelerated Test For Measuring Sulfate Resistance Of Hydraulic Cements Forcaltrans LLPRS Program. University Of California, 2000, p. 46, http://www.ucprc.ucdavis.edu/PDF/Accelerated%20Test%20for%20Meas.pdf. Accessed 19 Apr 2020.
Rangan, B. V. “Engineering properties of geopolymer concrete.” Geopolymers. Woodhead Publishing, 2009. 211-226.
Daman K. Panesar, in Developments in the Formulation and Reinforcement of Concrete (Second Edition), 2019
- Bai, in Sustainability of Construction Materials (Second Edition), 2016
Slag Cement Association. “Sulfate Attack”. Slagcement.Org, 2019, https://www.slagcement.org/aboutslagcement/is-07.aspx.
ASTM C452-19e1, Standard Test Method for Potential Expansion of Portland-Cement Mortars Exposed to Sulfate, ASTM International, West Conshohocken, PA, 2019, www.astm.org
ASTM C1012 / C1012M-18b, Standard Test Method for Length Change of Hydraulic-Cement Mortars Exposed to a Sulfate Solution, ASTM International, West Conshohocken, PA, 2018, www.astm.org
American Concrete Institute. “Certification Programs”. Concrete.Org, 2020, https://www.concrete.org/certification/certificationprograms.aspx.
NEW YORK STATE DEPARTMENT . Materials Method; FIELD INSPECTION OF PORTLAND CEMENT CONCRETE. NEW YORK STATE DEPARTMENT OF TRANSPORTATION MATERIALS BUREAU, 2012, https://www.dot.ny.gov/divisions/engineering/technical-services/materials-bureau-repository/mm92.pdf. Accessed 19 Apr 2020.