Keywords

1 Introduction

During construction of the highway, the route may pass through some areas where the soil or the water contain some H+ and some Cl− or SO42− [2]. The bridge is the main style to pass through the river or the valley. These ions will lead to corrosion during service item of the pile foundation of the bridge [3]. Harmful particles enter concrete from initial micro-cracks or internal pores of the concrete, corrode the internal structure of concrete through physical penetration and chemical action [5], and finally cause damage to the structure of concrete materials, especially in the chemical neutralization, which is more serious under acidic conditions.

Many scholars have systematically studied the durability of concrete and obtained lots of great progress and rich engineering experience and which put forward a feasible method to improve the durability of concrete [1]. Coating is a main method to enhance the durability of the concrete [4]. While, brush with anticorrosive paint is not a practical method because the pile foundation is under ground. From the perspective of the concrete material itself, adding admixtures or improving the variety of binders and other methods could increase the density and reduce the probability of initial cracks [6], and it also can promote their acid corrosion resistance.

Based on the investigation, analysis, and evaluation of the corrosive environment, the laboratory conditions are used to simulate the typical corrosive environment of acid chloride ions in the engineering site. This paper mainly investigates the deterioration rules of adding some admixtures into the concrete. The more dense of the concrete is, the better its anti-corrosion ability.

2 Material and Experiments

2.1 Materials

The cement is P.O 42.5 ordinary Portland cement and the properties are shown in Table 1. The fine aggregate is river sand with a fineness modulus of 2.8. The coarse aggregate is 5–31.5 mm continuous graded crushed stone, the mixing water is drinking water, and the water reducing agent is polycarboxylic acid. Water reducing rate of the water reducing agent is 20%.

Table 1 List of cement properties
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2.2 Mix Proportion

The mix ratios of 4 groups of ordinary concrete are designed, as shown in Table 2. The C group is the control group, the CH-1–CH-3 groups used to study the effect of admixtures on the corrosion and deterioration law of concrete. When mixing with concrete, the concrete slump is 200 ± 20 mm.

Table 2 The proportion of ordinary concrete (kg/m3)
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3 Experimental Section

3.1 Design of Simulated Test

The test solution was a NaCl solution with pH = 2 and a concentration of 6%. The cube blocks of 100 × 100 × 100 mm were made and cured to 28d age under standard curing conditions, then put into the corrosion solution, and the compressive strength was tested at 28, 56, and 90 d age.

3.2 Test Method

According to ISO 4012-1978 to test the compressive strength, the chloride penetration resistance was tested by the RCM method, and the pore structure parameters of concrete were tested by mercury injection test.

4 Analysis of Test Results

The appearance morphology, quality, strength, chloride penetration depth, and porosity of ordinary concrete and concrete with different proportions and types of admixtures under water curing and corrosion solution erosion were compared.

4.1 Morphology Changes

The morphology changes of concrete with different proportions and types of admixtures in a corrosive environment are shown in Fig. 1.

Fig. 1
3 close up views of concrete blocks labeled single fly ash, single ore powder, and fly ash and ore powder.

Influence of admixtures on appearance morphology of concrete

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It can be seen from Fig. 1 that the appearance morphologies of concrete with different proportions and types of admixtures are significantly different from those of ordinary concrete. In particular, the concrete mixed with ore powder is brown and has many black spots on the surface, which is the typical appearance characteristic of H+ and chloride ion erosion.

4.2 Variation of Intensity

Strength Variation

Test the compressive strength of concrete blocks in different ages of corrosion environment, and compare the strength changes. The compressive strength loss rate is used to represent the strength change of concrete after sulfate erosion, and the calculation method is as follows:

$$ \Delta CS = \frac{{CS - CS_{0} }}{{CS_{0} }} \times 100\% $$
(1)

∆CS—Loss rate of compressive strength;

CS—Compressive strength after immersion in a corrosive solution;

CS0—Compressive strength from water curing to age.

The strength changes of concrete with different proportions and types of admixtures in the corrosive environment are shown from Figs. 2, 3, and 4.

Fig. 2
A grouped column chart plots compressive strength versus soak time. It plots columns in groups of 0, 28, 56, and 90. The column for CH 2 is highest in all the groups.

Strength development law (water curing)

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Fig. 3
A grouped column chart plots compressive strength versus soak time. It plots columns in groups of 0, 28, 56, and 90. The column for CH 2 is the highest in all the groups.

Strength development law (acid solution)

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Fig. 4
A graph plots compressive strength versus soak time. It plots decreasing lines for C, C H 1, and C H 2.

Strength variation of admixture concrete in the corrosive environment

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As can be seen in Fig. 2, the strength of fly ash concrete specimens decreases obviously at an early age. However, the fly ash began to play the pozzolanic reaction and the strength increased in the later period, but the strength was lower than that of the ordinary concrete specimen group.

The strength of the sample group mixed with ore powder and concrete is improved at an early age, and which is mainly because the fineness of ore powder is finer than that of cement, and the gradation of concrete is improved, the pore structure of concrete is reduced, and the compactness is improved. At the later stage of hydration, the strongest growth effect brought by the improvement of compactness decreases, the mineral powder begins to play the pozzolanic reaction, and the strength of concrete continues to grow, showing a much higher strength than that of ordinary concrete.

In the early age of the fly ashore powder concrete specimen group, the strength of the concrete improved by the ore powder on the compactness increased significantly, and the strength was slightly higher than that of ordinary concrete. In the late hydration period, the ore powder and fly ash gradually played the pozzolanic effect, and the strength increased significantly.

As can be seen from Fig. 4, the strength of the fly ash concrete specimen group is lower than that of ordinary concrete at an early age, and which is also slightly higher than that of ordinary concrete in a later stage because fly ash begins to play volcanic ash effect in the later stage.

Due to the improvement of the density and pore structure of concrete by ore powder at an early age and the excellent pozzolanic effect at the later stage, the strength of the sample group of ore powder mixed with concrete is higher than that of ordinary concrete at each age, especially the improvement of the corrosion resistance of concrete at the later stage is particularly obvious.

The strength loss rate of fly ash mineral powder concrete specimen group at an early age is higher than that of ordinary concrete, and it shows better corrosion resistance in the later stage.

Change of Chloride Penetration Depth

The change of chloride penetration depth of admixture concrete in a corrosive environment is shown in Table 3.

Table 3 Change of chloride penetration depth of admixture concrete in the corrosive environment
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As can be seen from Table 3, the incorporation of fly ash has a certain inhibitory effect on the infiltration of chloride ions, the incorporation of ore powder has a significant inhibitory effect on the infiltration of chloride ions, and the incorporation of fly ash and ore powder has the same inhibitory effect on the infiltration of chloride ions as that of the single incorporation of fly ash.

Because the fineness of fly ash is finer than cement, the gradation of concrete is improved by adding fly ash, the pore structure of concrete is reduced, the compactness of concrete is improved, and the infiltration of chloride ions is inhibited. However, the improvement of pore structure and compactness of concrete is limited.

Mineral powder is a finer powder material than fly ash, which has a better effect on improving the pore structure and compactness of concrete and which has the strongest inhibition on chloride penetration.

Although both fly ash and ore powder can improve the pore structure and compactness of concrete, the micropores of concrete are limited, the improvement of pore structure and compactness after double mixing cannot be superimposed, and the infiltration effect of chloride ion is slightly better than that of single mixing fly ash.

Porosity Change

The porosity changes of admixture concrete in a corrosive environment are shown in Table 4 and Fig. 5.

Table 4 Variation of porosity of admixture concrete in the corrosive environment
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Fig. 5
A graph plots log differential intrusion versus pore size diameter. It plots mountain curves for c, c h 1, c h 2, and c h 3.

Variation of concrete porosity of admixtures

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As can be seen from Fig. 5, the pore size of the fly ash concrete specimen group is optimized to a certain extent. The pore content of 100–1000 nm decreases, while the pore content of 10–100 nm increases, mainly because fly ash has more particles with smaller particle sizes than cement. These particles fill the pore structure of concrete and also improve its compactedness.

The pore structure of the sample group of powdered ore concrete is significantly improved. Large pores not only transform into small holes, but the content of small holes is reduced, the result indicates that the particle size of powdered ore is much smaller than that of cement, and the pore structure of concrete is well filled after incorporation.

The fly ash and ore powder concrete specimen group combine the improvement effect of fly ash and ore powder on concrete pore structure in gradation. The content of small holes in concrete is the same as that of ordinary concrete, and the overall pore structure is fully optimized in the test.

5 Conclusions

This paper mainly investigated the influence of corrosion conditions, cementing material composition, cement type, and other factors on the law of corrosion and deterioration of concrete, and the main conclusions are as follows:

  1. (1)

    After the addition of admixtures, the content of 100–1000 nm holes in concrete can be significantly reduced. The improvement of corrosion resistance of concrete by single ore powder is the most significant.

  2. (2)

    The addition of fly ash significantly increases the content of 10–100 nm pores, and the strength is low at an early age, but the strong growth is limited at the later stage, which has a certain inhibition effect on the penetration of chloride ions.

  3. (3)

    After the addition of ore powder, the content of the 10–100 nm hole is significantly reduced, the strength of concrete is significantly improved, and the inhibition of chloride ion penetration is the most significant.

  4. (4)

    With the addition of fly ash and ore powder, the improvement of concrete pore structure in gradation is well combined. The content of pore in concrete is the same as that of ordinary concrete, but the overall pore structure is fully optimized, and concrete strength is improved, but the infiltration effect of chloride ion is slightly better than that of single fly ash.