Chemical composition of cement pore solutions
Abstract
The chemical compositions of the pore solutions extracted from seven different cement pastes (one Swedish and one French standard Portland cement, sulfate resistant, blast-furnace slag, fly ash, silica, and high alumina cement) have been determined. Analyses covered Na, K, Ca, Mg, Al, Fe, and Si as well as pH and Eh (redox potential). Ionic strengths in the range 0.03–0.29 M and pH-values in the range 12.4–13.5 were obtained. Only the pore solutions from the slag cement and the French Portland cement were reducing (negative Eh). The dominating cations of standard Portland, sulfate resistant, slag, silica and fly ash cement pore solutions were Na and K, and in sulfate resistant cement also Ca. The main components in the pore solutions of aluminate cement were Na and Al. The Si and Fe concentrations were low in all pore solutions.
References (7)
- R.S. Barneyback et al.
Cement and Concrete Research
(1981) - F.M. Lea
The Chemistry of Cement and Concrete
(1970) - P. Longuet et al.
Rev. des Mat. de Construction et des Traveaus Publics
(1973)
Cited by (236)
Impact of curing solution on concrete surface resistivity and formation factor
2024, Construction and Building MaterialsFormation factor (F) is the ratio of a concrete’s bulk resistivity to its pore solution resistivity and is inversely related to porosity and pore connectivity. Limitations of the unitless parameter F are of interest as measurements of concrete resistivity are increasingly common in research and could become part of performance-based concrete specifications. However, to avoid direct measurements of pore solution conductivity necessary to determine F, curing in a synthetic pore solution (i.e., “Bucket Test”) has been proposed. But, studies are lacking to support the implementation of this approach. To that end, this investigation compares surface resistivity (SR) and F results for seven concrete mixes based on two distinct curing solution regimes: (1) AASHTO TP119 Bucket Test (BT) curing and (2) conventional limewater curing. Formation factors for all mixes were calculated over the first 56-days of hydration to understand how the use of that metric, along with measurements of SR, influence interpretations of durability. NIST’s pore solution conductivity calculator was used to show that the BT’s synthetic pore solution is not an accurate proxy for mix designs including Class F or Class C fly ashes. Time-series SR measurements show that the choice of curing solution regime affects results, and therefore, how mixes can be compared with each other. Further, the percent difference between the calculated formation factors for the two curing regimes was at least 130% for all mixes at 56-days, showing that F as a metric can vary widely for the same mix design depending on the composition of the curing solution. The universal approach offered in AASHTO TP119’s default conditioning option attempts to simplify a concrete's F calculations by assuming the concrete's pore solution resistivity is the same as the synthetic curing solution's resistivity. However, creating and maintaining a synthetic pore solution increases the curing's experimental complexity, but does not enable any more accurate F calculations that would make the added experimental complexity worth it compared to the current industry norm of limewater curing. For this reason, the current industry standard curing condition – limewater curing – is recommended for formation factor calculations, including AASHTO TP119.
Characterisation of iron-rich cementitious materials
2024, Cement and Concrete ResearchIron is the fourth most abundant element in the Earth's crust, and cementitious materials are expected to contain iron-bearing phases, either in major or minor quantities. Iron-rich cement clinker is gaining attention because of its lower carbon footprint and higher sulfate resistance, while iron-rich resources are also increasingly being investigated as supplementary cementitious materials or as precursors for alkali-activated materials. However, iron-containing phases are among the least characterised in cementitious materials. This review paper discusses challenges in the characterisation of iron-containing phases for i) routinely used characterisation techniques, ii) specific characterisation techniques that excel at characterising iron-bearing phases, and proposes future areas of research to improve the accuracy and usability of these techniques. Micro-absorption, high X-ray and neutron scattering cross-section, fluorescence, and paramagnetism of iron can affect the application of X-ray diffraction, pair distribution function analysis, small-angle X-ray scattering, Raman spectroscopy, and nuclear magnetic resonance spectroscopy. X-ray absorption near-edge structure, extended X-ray absorption fine structure, 57Fe Mössbauer spectroscopy, and electron paramagnetic resonance spectroscopy are particularly suitable for characterising the iron oxidation states and local bonding environment in the iron-containing phases. UV–Visible spectroscopy, ion chromatography, and titration methods can be potentially used to quantify iron concentration and oxidation states in aqueous solution, but further research is required to apply them in the field of cementitious materials.
Gold-sputtered LPG fiber sensor pulse electroplated with iron-carbon for monitoring passivation and depassivation of carbon steel in concrete pore solutions
2024, Cement and Concrete CompositesMonitoring the passivation and depassivation of reinforcement steel is of significant importance, particularly for certain reinforced concrete structures that define the time of steel rebar depassivation as the end of the durability service life. In this study, a gold-sputtered long-period grating (LPG) optical fiber sensor coated with pulse-electroplated iron-carbon is characterized for continuous monitoring of the surface state of carbon steel from passivation to depassivation in concrete pore solutions. Electrochemical corrosion and optical tests are performed simultaneously using an electrochemical workstation and an optical instrument. A protective passivation film with a thickness of approximately 4.05 nm was formed on the iron-carbon coating after 5 days of immersion in the simulated concrete pore solution, and its thickness is nonlinearly correlated with the wavelength shift of the LPG optical fiber sensor during the passivation process. The resonant wavelength changes in the opposite direction after depassivation, which can be used for the detection of the depassivation time. After depassivation, the wavelength shift and mass loss of the iron-carbon coating can be divided into three phases, and a linear relationship exists in each phase. The gold-sputtered fiber sensor coated with pulse-electroplated iron-carbon investigated in this study, demonstrates better performance than silver-deposited LPG fiber sensors.
Influence of AgCl film resistance on stability and potential response of Ag/AgCl chloride-sense electrode in simulated concrete pore solution
2024, Electrochimica ActaThe characteristics of AgCl film determine performance of Ag/AgCl electrode for chloride detection in concrete pore solution. In this study, the microstructure effect of AgCl film on the durability and sensitivity of Ag/AgCl electrode was investigated by electrochemical methods with SEM. The results indicated generally thick and dense AgCl film resulted in the improved service life and prolonged response time of Ag/AgCl electrode. Further, potential fluctuations were relevant for AgCl film thickness>32.04 µm. Based on the obtained data, the relationship between AgCl film resistance and service life/response time of Ag/AgCl electrode was established, which can accurately evaluate the performance of Ag/AgCl electrode in concrete.
Effect of sand coating on durability and micro-structural deterioration of GFRP rebar under alkaline environment attack
2024, Construction and Building MaterialsThe objective of this study is to investigate the consequences of the sand-coated layer on the durability of glass fiber reinforced polymer (GFRP) rebars under four alkali solution concentrations and three temperatures. A total of 464 GFRP rebars specimens were manufactured to undergo accelerated corrosion experiments and mechanical performance test. Among them, 438 specimens were used to test the residual tensile strength of GFRP rebars after 120 days of immersion; 26 specimens were applied for surface observation and microscopic testing to analyze the degradation and damage process of GFRP rebars. SEM and digital camera were used to examine the micro-structure of samples either with or without sand layer covering. The unidirectional tensile strength experiment was conducted to test the remaining tensile strength of GFRP rebars after corrosion. The experimental results indicate that sand coating provides better protection and restraint in GFRP rebar durability reduction, resulting in a lower rate of fiber loosening and resin cracking and flaking when exposed to a solution over a pH of 12.5. As the failure of GFRP rebars ranges from local damage to cracking of the peripheral sand protective layer, the pH value of 12.5 is considered a critical alkali solution concentration. Based on experimental results, an improved model was proposed to predict the short-term and long-term residual strength values of GFRP rebars. The calculation results indicate that the predict values are in good agreement with the experimental ones, and the proposed model can be used to predict the residual strength of GFRP rebars.
Reactivity and leaching potential of municipal solid waste incineration (MSWI) bottom ash as supplementary cementitious material and precursor for alkali-activated materials
2023, Construction and Building MaterialsThis work evaluated the reactivity and leaching potential of municipal solid waste incineration (MSWI) bottom ash as supplementary cementitious material (SCM) and precursor for alkali-activated materials (AAM). The chemical composition of the amorphous phase in MSWI bottom ash was found to be in the same range as that of Class F coal fly ash. The reactivity of MSWI bottom ash as SCM and AAM precursor was tested to be much lower than that of blast furnace slag, but similar to that of Class F coal fly ash. The method of thermodynamic modeling was found useful in providing references for the mix design of MSWI bottom ash-based AAM. Grinding MSWI bottom ash into powder for the application of SCM and AAM precursor increased its leaching potential. Based on the findings of this study, recommendations were provided on how to use MSWI bottom ash to prepare blended cement pastes and AAM.