First, using a 25 mm calcium solution was poured into a 250-mL conical bottle and this solution mixed with 100 mL of distilled water. Second, we added the sodium hydroxide 10% with pH = 10 (test by litmus). Then, 0.02 G murexide was added and dollied continuously to reach komplexon III solution (0.05 M solution) until the solution changed from red to purple. Calcium ion content ( C a 2 + ), milligram/liter (mg/L) is calculated by the Eq. 1 below: X 8 = V 1 . T . 1000 . 1000 V , (1)

where V ₁ is the volume of komplexon III solution used to indicate titration in milliliters (mL); T is titration of komplexon III solution in gram/mL with calcium ion (C_a ²⁺); and V is water volume in mL. Results show in Eq. 1; Figure 5.

Distilled 25 mL of water was used for calcium and magnesium contents with 800 mg/L. Next, we poured this solution into the 250-mL conical bottle. This solution was mixed with 100 mL distilled water, and sodium hydroxide 10% with pH = 10 (test by litmus) was added. We continuously dolled 0.02 g Eriochrome Black T to reach komplexon III solution (0.05 M solution) until the solution changed from red to blue.

Magnesium ion content (Mg ²⁺), mg/L was calculated by the Eq. 2 below: X 9 = V 2 − V 1 . T . 1000 . 1000 V , (2)

where V ₁ is the volume of komplexon III solution used to indicate the titration total of calcium and magnesium in mL; V ₂ is the volume of komplexon III solution only using T = 20 V . 0 , 0020 titration 20 mL of calcium chloride in mL; T is titration of komplexon III solution in g/cm³ with magnesium (Mg ²⁺); and V is water volume in mL. Results show in Eq. 2, Figure 5.

+ Material (chemistry)

We used chemical hydrochloric acid (HCl) ratio 1:1 and hydroxylammonium clorua 10% solution by dissolving 10 G NH₂OH.HCl in 100 mL of distilled water. pH = 5 solution was achieved by dissolving 175 g Natri acetate CH₃COONa in 150 mL distilled water and 450 mL concentrated acid acetic (CH₃COOH) in distilled water to make up the solution of 1,000 mL. We continuously shook the mixture well, then added phenanthroline 0.1% solution (dissolve 0.1 g 1,10-phenanthroline monohydrate (C₁₂H₈N₂.H₂O)) to 80 mL distilled water, dolled it, and heated to 800 C. It did not boil, and we then used the distilled water to make a stable 100 mL. We next added 500 ppm iron storage solution (dissolve 1.7594 g Fe(NH4)₂(SO4)₂.6H₂O in the distilled water and then slowly add 5 mL H₂SO₄ concentrated and mix evenly). The solution was protected at 28°C. We then poured 500 ppm iron storage solution into the bottle to make up to 10.00 mL, and added the distilled water up to the mark (1 mL = 10.00 mg Fe).

+ Devices and instruments

The glass bottle was cleaned with HCl concentrated solution to completely remove iron that was still attached to the wall before use. Also required were a 100-mL glass Erlenmeyer bottle, 50 mL glass tube, 100 mL volumetric flask (glass bottle), a spectrophotometer (S-921/Digital Visible), and an electric stove.

+ Implementation Process

Samples were acidified with pH < 2 before analysis, using 50 mL samples poured into Erlenmeyer bottle (samples must be mixed evenly). If the sample volume of iron contents was higher than 1 mg, it was diluted to 50 mL. We then added 2 mm HCl (ratio 1:1) and 1 mL NH₂OH.HCl. After adding a few pills to the Erlenmeyer, it was necessary to boil it in 15 mL volumes. They were continuously kept at 28 °C and the solution was poured into a 100 mL volumetric flask. Next, we added 10 mm pH = 5 solution and 1 mL 1,10-phenanthroline solution.

The distilled water was then added up to marly and dolled evenly to maintain stability for 10 min to obtain the best colors and maximum stability. Finally, absorbance was measured on a spectrophotometer (S-921/Digital Visible) with a wavelength of 510 nm.

+ Calibration curves

Using solution with mL = 10 mg Fe concentration, we prepared a series of iron standard solutions according to Table 1 and Figure 2.

Measurement of a series of absorbances of the samples resulted in the diagram A = f(C), which uses the method of least squares to reach the equation y = ax + b. From the value of absorbance samples solution by spectrophotometer (A), concentration value (C) can be inferred. Results are shown in mg/L in Table 1 and Figure 2.

The experimental method for investigating the effect of epoxy for protecting reinforced concrete from chemical erosion was achieved by adding nanoparticles of Fe₂O₃ into a carbonaceous matrix. The results show more than 3% of mixed mass with coatings, which remarkably supports concrete surface erosion and limited aging process and solubility (Dorado et al., 2023).

+ Determination condition of Cation Na⁺ và K⁺

The determination of cation Na⁺ và K⁺ with method condition is 0.1 up to 10 mg/L and 10 μL circle sample. All of these cations were detected by measuring conductivity (washing solution should have a small enough conductivity). The temperature of the bottle in the “detector” needs to be stabile within ±0.1°C. Cation concentrations are determined in “calibration curves.” The resolution (R) of the column is determined by the non-low peak R = 1.3.

+ Sample and material (Use hydrochloric/DAP acid eluent)

We dissolved 5.2 mL solution of hydrochloric acid (c(HCl) = 7.7 mol/L) and 0,562 g ± 0,006 g of Diaminopropionic monohydroclorua (DAP) acid (C₃H₈N₂O₂⋅HCl) into the 100 mL volumetric flask (glass bottle) with degassed water. The solution contained 0.04 mol/L hydrochloric acid and 0.004 mol/L DAP. Solution was protected at 4 °C – 6 °C and replaced every 7 days. Samples were kept in sealed containers and filtered (pore size 0.45 μm), with correct pH up to 3 ± 0.5 by nitric acid (c(HNO₃) = 1 mol/L) to avoid precipitation, sample contamination, or cation metabolism by microbial growth. Immediate analysis was necessary after 24-h sample protection to obtain the best results.

+ Devices and instruments

We used the ion chromatography system Ion Dionex 3000 (high-performance liquid chromatography—HPLC; see Figures 3, 4) by quality requirements (separation column must ensure separation conditions and not obstruct the cations; concentration of Na⁺ is 1 mg/L; K⁺ is 2 mg/L). A polyethylene container was used to store the washing solution. We also used a pump, sample injection system with sample loop (10 μL), separation column with separation efficiency, front column, conductivity detector (uncompressed), recording device, and a polyethylene column containing non-polar phase for pretreatment of samples. We observed from the samples and solution which had high standard concentration that the resolution (R) of the column was determined by the non-low peak R = 1.3 . Results show in Eq. 3 and Figure 4, and any part of peak “pic”: R 2 , 1 = 2 t R 2 − t R 1 W 2 + W 1 , (3) where R _2,1 is the resolution par of peak “pic” 2.1; t_R1 is the storage time of peak “pic” 1 in seconds (s); t_R2 is the storage time of peak “pic” 2 in seconds (s); W 1 1 is the peak width of peak “pic” 1 on the time axis in seconds (s); and W 2 1 is the peak width of peak “pic” 2 on the time axis in seconds (s).

+ Implementation process

We used the ion chromatography instrument Ion Dionex 3000 for calibration, normalized by first-order normalization function. The first-order standard formula to determine the ions is Y i = b i . ρ i + a 0 , i , (4) where Y i is the measured value, the height of the peak “pic” in millimeters (mm); b_i is the slope of the standard function in millimeters.liter/milligram (mm.L/mg); ρ i is iron concentration “i” in mg/L; a_0,i is the point of the normal function intersecting the vertical axis in mm.

We measured the samples and white solution by filling a 100 mL flask with water and adding 0.1 mL of nitric acid solution (c(HNO₃) = 1 mol/L. After setting up the standard function, we injected the prepared sample into the chromatograph and measured the peak “pic.” (Note: if the ion concentrations in the sample to be analyzed exceed the calibration range, dilute the sample and then analyze). Next, it was necessary to exactly check the standard function and measure the two solutions with the lowest and highest locations in the working areas. A series of samples were measured at any time every 20 measurements. Calculation of the calibration solution concentration was analyzed by the first-order function.

Concentration ( ρ i ) in mg/L of solution cation calculated in the peak “pic” and the inverse first-order standard function: ρ i = Y i − a 0 , i b i , (5) where all of the units in the above formula are the same as for Eq. 2. The final results are shown in Eqs 3, 4; Table 1 and Figure 5.

We added two drops of Komplexon III solution to 50 mL water and then mixed well. Next, 1 mL of Nessler reagent was added and mixed. After 10 min, we measured the color intensity of the solution using a photoelectric colorimeter. We consistently used a purple filter (diameter O = 400: 425 mm), cuvette dày 1–5 cm (note, after 30 min of showing colors, colors must not change).

Content ion ammonia ( NH 4 + ), mg/L is calculated by Eq. 6: X 16 = C 50 V , (6) where C is ion ammonia concentration, as read on the standard diagram, in mg/L; V is water volume in mL; the volume of diluent water is 50 mL.

The results of analysis of cation (TCVN 6660:2000) showed 82.33 milli/liter, and 4.366 mg actual/liter and 100% milligram/liter of total ions. The relationship of the conversion unit calculating cations, such as Ca²⁺, Mg²⁺, Fe³⁺, Fe²⁺, Na⁺, K⁺, an NH⁴⁺, showing these values were converted, including percentage of mg/L, actual mg/L, and mg/L (see Figure 5; Eqs 1–6).

We poured 100 mL water into a 250-mL conical glass bottle and then added potassium chromate (Kali chromate) 1 mL solution with 5% content. Next, we added agentum nitrate 0.05 N solution to ensure calibration and observed the mixture until it precipitated and became orange-red. This was done twice to obtain the average value.

Ion chloride (Cl⁻) content, mg/L is calculated by Eq. 7: X 19 = V 1 . N . 0 , 03546.1000 1000 V , (7) where V ₁ is the volume of agentum nitrate 0.05 N solution used as a measurement of the calibration in mg/L; N is the equivalent concentration of agentum nitrate solution; 0.03546 is the value of the equivalent concentration of chloride milligram; V is the volume of water in mL. The results show in Eq. 7; Figure 6.

However, an experiment was conducted to determine the erosion of seaside concrete structures by the Cl⁻ and carbonate processes. The research used 5% NaCl and Cl-free particles which showed two factors to evaluate concrete erosion. The microstructure of concrete particles was analyzed by SEM (scanning electron microscope) and XRD (X-ray diffraction). The results clearly showed that nanoconcrete decreases the carbonate process in the same cycle. The contents of nano-SiO₂ and nano-ZnO are 2%, and 1% are lower than 19.3% and 17.6% compared with normal concrete. The glue of C-S-H made the internal structure of concrete thickness, so adding nano-SiO₂ and nano-ZnO prevents the erosion process of Cl⁻ and carbonation, thus increasing sea concrete safety (Maohua et al., 2023).

Research on the erosion speed of steel into concrete used nano-Ag/AgCl to measure ion Cl concentration on the reinforcement concrete surface and open-circuit voltage of the primary battery and calomel, while the theory of chloride diffusion and open-circuit voltage is used to investigate the erosion process. The results show maximum erosion speed after 15 h and that the cavity of reinforced concrete was proportional to chloride ion in the environment (Yixiao et al., 2023).

We poured 50 mL solution SO 4 2 − into a heat-resistant cup (or Becher). The mixture was then diluted to 100 mL. Next, we added four drops of metal–organic-red and hydrochloric acid (HCl ratio 1:1) until the solution was a pink-brown color. We continuously boiled this mixture and mixed in evenly a drop (10 mL) of bari chloride 10%. It was then boiled for 5 min. We covered the beaker with a watch glass, then placed it in a water bath for 4 h for the barium sulfate to precipitate. We continued filtering the mixture with ashless filter paper, washing the precipitate on the filter paper with hot diluted (1 + 99) hydrochloric acid.

After that, we washed it with hot distilled water until the chloride ion in the washing water was gone (note: wash water does not precipitate when agentum nitrate is added). The filters containing bari sulfate with determined mass were put in a cup and then dried at 105°C, burned and heated at 800°C for up to 40 min, then the temperature was stabilized in a desiccator and it was weighed until constant weight.

Ion sulfate ( SO 4 2 − ), mg/L was used by the Eq. 8 below: X 11 = G . 0 , 4115.1000 1000 V , (8) where G is the mass of precipitation of bari sulfate in g; 0.4115 is the factor converting the mass of barium sulfate to SO⁻¹; V is the volume of water in mL. The results show in Eq. 8 and Figure 6.

However, a combination of the three methods evaluating sulfate and carbonation affection in concrete showed mass changes, characteristics, and clear forms. On the other hand, the microstructure of characteristics and forms of concrete erosion were clearly revealed by SEM (ESEM-EDS), máy infrared spectrum Fourier (FTIR), and XRD. The results showed the surface characteristics deformed clearly with carbonation time and sulfate affection. Moreover, the relative intensity and mass gradually increased with carbonation time (Chen et al., 2023).

Ion bicarbonate content (HCO₃ ⁻) and carbonate (CO₃ ²⁻) were determined to determine total and free alkalinity (Table 2).

We experimentally measured the affection the freeze–thaw (F–T) cycles and compound-salt attack for deformed characteristics and microstructures of hybrid fiber reinforced concrete (HFRC). The results showed that the F–T cycles and compound-salt of polypropylene hybrid fiber affected forms and limited mass, relative elastic modulus (RDEM), mechanical reliability, and compressive–flexural strength. On the other hand, pore volume was bigger than 1,2HFRC after F–T salt cycles (Dongtao et al., 2023).

The experimental method used corn-straw fiber (CSF) to add concrete components to prevent erosion by chloride ion attack. A rapid chloride permeability test (RCPT) and rapid chloride movement (RCM) were designed to evaluate the change of ion resistance of reinforcement concrete. Water-absorbed speed (WAR) and mercury penetration porosity (MIP) were used to support information on microstructures. The results show that adding Na₂SiO₃ of CSF increased strength by 15.7%, 17.8% và 33.4%, whereas absorbed water of CSF and the alkaline environment by Na₂SiO₃ supply good conditions for the hydration process and decrease of chloride ion movement. Cellulose contained in CSF with the hydroxyl and carboxyl group help improve the chloride ion resistance of concrete by low weak electrical conductivity and ion exchange binding force (Zhipeng et al., 2023).

The results of anion analysis (TCVN 6660:2000) show 201.03 mg/L but 4.366 mg/L and 100% mg/L of the total of ion. Comparison of the conversion units calculating anions, such as Cl⁻, SO₄ ²⁻, HCO₃ ⁻, and CO₃ ²⁻, and showed that the conversion of these values included a percentage of milligram per liter, milligram actual per liter, and milligram per liter.

However, the analytical methods of atomic absorption spectrometry, SEM-EDS, nano-indentation, polarization, and macroscopic mechanical testing were used to investigate erosion by chloride. The results’ flexible durability decreased remarkably up to 47%. The elastic modulus and the nano-stiffness are eroded differently approximately 30–189 GPa and 0.16–6.41 GP (Zhaoping et al., 2023).

We poured 100-mL water into the titration flask and then add 0.5 g potassium sodium tartrate comminute. Next, 0.2 mL phenolphthalein solution was added, mixed evenly, and titrated with sodium hydroxide 0.1 N. This solution was then continuously observed until it was a sustainable pink color (note: to avoid lost carbonate, it was necessary to pour water into the bottle and then close the stopper immediately after filling was complete). This was done twice for this experiment. The water volume at the first and second times was similar. We then added the same amount of sodium hydroxide 0.1 N twice. After adding sodium tartrate 0.2 mL, phenolphthalein sodium, and titration by sodium hydroxide 0.1 N until a sustainable pink color, the results were recorded for two titrations.

Free carbon dioxide (CO₂) (mg/L) is used in the formula below: X 3 = V t . N . 0 , 044.1000 . 1000 V , (9) where V _t is the volume of sodium hydroxide 0.1 N used for titration mL; N is the concentration of sodium hydroxide solution; 0.044 is the concentration of CO₂ in mg; and V is water volume in mL. The results show in Eq. 9 and Figure 9.

However, the experimental research used approximately 2–4% nano-silica to investigate the hydrate capability, strength, durability, and microstructure of concrete. The results show an increase in the percentage of nano-silica which made changes in the physical and mechanical properties, and microstructure density and a decrease of the erosion process (Fadi et al., 2023). On the other hand, the influence of alkaline silicate reaction (ASR), hydration, and fly ash mixed with nanoconcrete material created compressive and flexible strength, clearly limiting erosion (Yanjin et al., 2023).

We poured 100 mL of water saturated with calcium carbonate into a 250-mL beaker. We then added three drops of methyl orange-red and titrated with hydrochloric acid (HCl) 0.1 N until the solution changed from yellow to orange-red color.

CO₂ corrosive content (mg/L) uses the Eq. 10 below: X 1 = V 2 − V 1 . N . 0 , 022.1000 . 1000 V , (10) where V is the volume of hydrochloric acid (HCl); 0.1 N used for the titration of the saturation sample calcium carbonate in mL; V ₁ is the volume of hydrochloric acid (HCl); 0.1 N used for the titration of total alkalinity in mL; N is the concentration of (HCl) 0.1 N; 0.022 is mg of CO₂; V is the volume of water in mL. The results show in Eqs 10–14 and Figure 9.

Experimentation was used to determine the affection degree of temperature, water evaporation, and airspeed to CO₂-absorbed process by consideration of Na₂CO₃ and K₂CO₃. The results showed that K-based absorbent is rather than Na-based absorbent which obtained at 50°C temperature with 90 mbar H₂O. And it is only keeping 2% of the total volume in tight areas (Itzel et al., 2021). Comparison with CO₂ absorbed volume in 2023 obtained 170,726 CO₂-eq per day (Rafael et al., 2019).

- Drying residue content is at 105 C

We poured 200 mL water into a porcelain cup and then gradually evaporated it at 105 C for drying. We next weighed it under constant weight on the electric stove until completely dry. The porcelain cup contained dry residue within 2 h at 105 C, and then the temperature stabilized in the desiccator and was quickly weighed to constant weight.

Dry residue content t 105°C (mg/L) used the formula below: X 17 = G . 100 . 1000 V , (11) where G is the dry residue at 105°C in grams and V is the volume of water in mL.

- “Insoluble” residues content dried at 105°C

Use 200 ml water which is a water test filter by filter paper, dried at 105°C temperature, and then weighted to constant weight. Filter paper contains dried residue after 2 h at 105°C temperature. Next, measure the temperature in the desiccator and quickly weighted it to a constant weight.

“Insoluble” residue content (mg/L) dried at 105°C used the formulas below: X 18 = G . 100 . 1000 V , (12) where G is insoluble residues content dried at 105 C in grams and V is the volume of water in mL.

- “Insoluble” residue content burned at 600 C.

The filter paper contained insoluble residue at 105 C (insoluble residues are determined in Eq. 9). This was poured into a porcelain cup, the weight determined, and then was burned at 600 C for 1 h. Finally, the temperature in the desiccator and quickly weighed to a constant weight.

Insoluble residue content (mg/L) burned at 600 C temperature is determined by the formula below: X 20 = G . 100 . 1000 V , (13) where G is “insoluble residue content dried at 105 C and the amount of remaining residue after heating at 600 C in grams, and V is the volume of water in mL.

We used a mixed color indicator to measure pH. Each color indicator had a narrow range of 1–2 pH. When using the mixed color indicator, the pH range converted color more widely. The methyl orange was measured (0.2% bromothymol blue solution with 0.1%). Next, part of the solution volume of methyl red was mixed with two parts of the solution volume of bromothymol blue. The mixed color indicator had a range of 4–8 pH. We used sodium hydrogen phosphate solution (0.2 M), nitric acid (0.1 M), and calci phosphate solution with a pH range of 3.0–8.0 (Figure 7). Cr ions and carbonation in reinforced concrete were used to determine the alkalinity and microstructure materials. The results showed that the carbonation process increased gradually with pH = 11, compared with no carbonation with pH = 12.6. X-R diffusion and Mott–Schottky show Cr and Fe oxides/hydroxides independent of the alkaline environment of reinforcement concrete. Conversely, Cr oxides will weaken the passive capability of reinforcement. Thus, erosion process would occur quickly (Gongnian et al., 2023).

Use 50 ml water pour into an Erlenmeyer flask. Next, we added 1 mL sulfanilic acid solution and mixed evenly. It was stabilized for 5 min and then 1 mL 1-naphthylamine sodium was mixed in. It was continuously stabilized with 40 min. The sample solution intensity was measured by the spectrophotometer (S-921/Digital Visible). A green filter was then used (O = 520 mm, cuvettes 1–5 cm thick).

Ion nitrite content (NO₂ ⁻), mg/L unit is determined by the formula below: X 14 = C 50 V , (14) where C is the concentration of nitrite read on the titration diagram in mg/L; V is the volume of water in mL; 50 is the volume of water dilution in mL. The results show in Eq. 14 and Figure 9.

We added 1 mL solution of salicylate sodium to 10 mL water and evaporated it in a porcelain water bowl on a water bath until dry. After cooling, we added 1 L of sulfuric acid. The cup was stirred with a glass rod along its sides and bottom until the residue was completely dissolved, and stability maintained for 10 min. We then poured distilled water into the cup and mixed evenly. It was then poured into a 50-mL Erlenmeyer flask. The cup was washed many times and this water poured into the flask. Next, we added 7 mL sodium hydroxide 10 N solution and evenly mixed the distilled water up to mark level.

Ten minutes after adding sodium hydroxide 10 N solution, the solution color did not change because use color intensity is measured by the spectrophotometer (S-921/Digital Visible) machine; it uses a purple filter (O = 410 mm) cuvette 5 cm thick.

Ion nitrate content (NO₃ ⁻) (mg/L) was determined by the formula below: X 15 = C 50 V , (15) where C is the nitrate concentration read on the chart in mg/L; V is volume of water in mL; 50 is the volume of the color-determination water in mL. The results of the special item analysis with total hardness and alkalinity are shown in Figure 8.

We reduced the alkalinity of 100 mL water with hydrochloric acid 0.1 N; the amount of acid consumed as total alkalinity titration. Next, 5 mL solution of 0.2 g Eriochrome Black T and komplexon III solution titration was added until the color turned from red to blue.

Permanent hardness (with the regulation of German degree guidance) is determined by the formula below: X 6 = V 1 . T . 100 . 1000 V , (16) where V ₁ is the volume of komplexon III solution used for titration in mL; T is titration of komplexon III solutions with calcium oxide (CaO) in g/mL; V is the volume of water in mL. The results show in Eqs 15, 16 and Figure 9.

We poured 100 mL water into a 250-mL Erlenmeyer flask bottle. Next, we added rock or gravel particles and then boiled until one-third of initial volume remained. The precipitate of calcium carbonate and magnesium carbonate was washed several times with boiled and cooled distilled water to make 100 mL of filtered water. Three drops of methyl orange color were added to the water to obtain titration by hydrochloric acid 0.1 N until the color changed from yellow to orange-red.

Carbonate hardness with German degree regulation (1⁰ of German = 10 mg/L of calcium oxide (CaO) was determined by the formula below: X 5 = V 1 − V 2 . N . 0 , 02804.1000 . 1000 V , (17) where V ₁ is the volume of hydrochloric acid solution used for titration with total alkalinity in mL; V ₂ is the volume of hydrochloric acid solution used for titration with carbonate and bicarbonate alkalinity in mL; N is the concentration of hydrochloric acid; 0.02804 is mg of calcium oxide (CaO); and V is the volume of water in mL. The results show in Eqs 16, 17 and Figure 8.

Because the water had pH < 8.3, it was not necessary to determine free alkalinity, but it was useful to calculate total alkalinity. We poured 100 mL water into a 250-mL Erlenmeyer flask bottle then added three drops solution of methyl orange color and titration hydrochloric acid 0.1 N. We observed the mixture until it changed from yellow to orange.

Total alkalinity X₂ (milligram/liter, mgdl/L) is determined by the Eqs 18, 19 and Figure 8: X 2 = V 2 . N . 1000 V , (18) where V ₂ is the volume of hydrochloric acid solution 0.1 N used for titration with orange indicator color in mL; N is the concentration of hydrochloric acid; and V is the volume of water in mL.

Results of the special item analysis are shown in Figure 9.