Study on compressive strength and sulfate corrosion resistance of limestone powder and waste glass powder mixed concrete

In order to enhance the utilization rate of waste powder and improve the sulfate corrosion resistance of limestone powder concrete, the evolution law of compressive strength, porosity, sulfate corrosion resistance of limestone powder and waste glass powder mixed concrete with different proportions was studied. It is found through that the early strength of limestone powder concrete cannot be enhanced by waste glass powder, but its late strength can be improved (curing age of 90d). The compressive strength can be improved by adding 5% ~ 15% waste glass powder to the concrete with 10% limestone powder or 5% waste glass powder to the concrete with 20% limestone powder. The pozzolanic activity of waste glass powder is the main factor to increase the late strength of limestone powder concrete. Waste glass powder can be used to improve the sulfate corrosion resistance of limestone powder concrete, and the best combination is 10% limestone powder concrete mixed with 5% waste glass powder. The corrosion products showed that waste glass powder could improve the sulfate resistance of limestone powder concrete from the following three aspects: consuming part of CH, reducing the degree of sulfate corrosion reaction, and improving the limestone powder to inhibit the later hydration reaction of concrete. This study provides a valuable reference for the further utilization of limestone powder and waste glass powder.


Introduction
The concrete industry generates severe environmental problems [1].Cement manufacture is an energyintensive and highly-polluting process that contributes about 5~8% to overall carbon dioxide (CO 2 ) emissions [2][3][4][5].One of the primary study areas of the sustainable development of concrete materials is the use of waste powder [6,7] to replace some of the cement.At present, limestone powder concrete [8,9] has become a research hotspot because of its excellent mechanical properties, reasonable economic effects and broad engineering application prospects.Studies [10,11] have demonstrated the primary nucleation, filling, dilution and chemical action mechanisms of limestone powder in concrete.The mechanical characteristics, water permeability resistance and chloride ion permeability resistance of limestone powder concrete would be improved with the increase of limestone powder dosage when limestone powder is mostly exhibited as nucleation, filling and chemical action mechanisms.The mechanical characteristics, water permeability resistance and chloride ion permeability resistance of limestone powder concrete would decrease with the increase of limestone powder dosage when limestone powder is mostly exhibited as dilution.
In some water conservancy projects in China, limestone powder is used instead of fly ash to prepare low hydration thermal concrete and build dams [12].Zhang et al [13] found that a small amount of limestone powder could improve the compressive strength of lithium slag-UHPC at all ages, and that a dosage of 10% was the most significant, which offered advantages in terms of environmental protection and sustainable development.Demirhan et al [14] investigated the performance of self-compacting mortars composed of highvolume limestone powder.The test results showed that slump values increased while pointing out a satisfactory fresh property in accordance with an increase in the replacement level of limestone powder.However, in research and engineering applications, it is generally found that limestone powder can be used to reduce the sulfate resistance of concrete [15,16].Because limestone powder can provide carbonate ions necessary for the formation of carbonite, and concrete mixed with limestone powder is susceptible to TSA (calcium carbonite silicate type) failure under prolonged sulfate attack at a low temperature (<15 °C) [17], the use of limestone powder is limited to some extent.
In the majority of conditions, limestone powder merely has filling effect because it lacks the pozzolanic and self-cementing property [18,19].At present, the reasonable dosage of limestone powder in concrete is generally no more than 15% [20], which greatly limits the utilization rate of limestone powder.As a result, several researchers [21,22] suggested creating ternary or multicomponent cementing materials by combining limestone powder with additional mineral admixtures, providing a great idea.Lima-Guerra et al [23] succeeded in producing concrete by mixing limestone powder with bentonite.Celik et al [24] found that the performance of limestone powder and fly ash mixed concrete was better than that of limestone powder concrete, with the optimal ratio of limestone powder and fly ash obtained based on a dynamic hydration model.According to Wang's research findings [25], the strength and self-shrinking performance of the limestone powder-fly ashcement ternary cementing system were superior to those of the fly ash-cement binary cementing system,       whereas those of the limestone powder-slag-cement ternary cementing system were marginally inferior to those of the slag-cement binary cementing system.However, fly ash and other high quality mineral admixtures are currently experiencing issues like shortages and price increases [26], so, it's critical to find a less expensive option to combine with limestone powder.China is a major producer of glass, and waste glass powder in glass production is usually disposed by backfilling or open  air stacking, which is not conducive to the ecological environment [27].Studies have demonstrated that [28] waste glass powder, similar to fly ash, has small particles, a large specific surface area and certain pozzolanic activity, which can be used in concrete manufacturing.A long-term performance test of concrete manufacture using a large amount of waste glass powder in place of cement was carried out by Du et al [29], which demonstrated that, compared with pure cement concrete, all concrete containing waste glass powder exhibited excellent mechanical properties at the curing age of one year, and that concrete containing 15% of waste glass powder had the highest strength, which was about 27% stronger than pure cement concrete.Matos et al [30] substituted waste glass powder for some of the cement (0%, 10% and 20%) to prepare mortar, who then tested the resistance of the mortar to external sulfate attack and chloride ion penetration.The study discovered that as the dosage of waste glass powder grew, so did the mortar resistance to chloride ion permeability.Mortar containing 10% waste glass powder exhibits the greatest resistance against sulfate attack from the outside.The effect of waste glass powder on the drying shrinkage performance of cement mortar was examined by Patel et al [31].The findings revealed that waste glass powder would not absorb free moisture in mortar, and that such non-absorbability would cause mortar to slowly expand.A 20% waste glass powder mixture could prevent 3% of shrinkage or expansion.Jiang et al [32] investigated the sample size effect of waste glass powder and ground blast furnace slag-based geopolymer pastes cured at different conditions and ages on their physical properties and micro-characteristics, further promoting the green development of concrete and the use of waste glass powder.
Concrete that contains both waste glass powder and limestone powder has yet received comparatively little research.For a higher substitution rate of cement, we suggest manufacturing concrete by combining waste glass powder with limestone powder.It is expected that the promoting role of limestone powder on the early strength of concrete and that of waste glass powder on its middle and late strength can be played at the same time.Improving the sulfate corrosion resistance of limestone powder concrete.Maximize the resource utilization of limestone powder and waste glass powder.Reduce carbon dioxide emissions in concrete production and solve the pollution problem of waste powder.The compressive strength of concrete containing waste glass powder and limestone powder of various proportions and curing ages was examined in this study.The MIP (mercury intrusion porosity method) was used to test the pore structure of concrete containing waste glass powder and limestone powder of different proportions and curing ages.Finally, the change mechanism of the compressive strength of concrete containing waste glass powder and limestone powder was examined from a microscopic angle.Considering the common problem of the poor sulfate corrosion resistance of limestone powder concrete, we studied the sulfate corrosion resistance of concrete mixed with limestone powder and waste glass powder of various proportions using a modified low temperature test chamber.After a low temperature sulfate corrosion test, the corrosion products of concrete combined with waste glass powder and limestone powder of various proportions were determined using TG-DSC (simultaneous thermal analysis).In addition to increasing the substitution rate of waste powder (limestone powder and waste glass powder) for cement, the sulfate erosion resistance of limestone powder deteriorated concrete can be improved, which serves as a guide for the sensible use of waste glass and limestone powder in concrete.

Raw materials 2.1. Cement
The PO 42.5 Portland cement from Wuhan Huaxin Cement Company with a specific surface area of 360m 2 /kg, a density of 3.15 g cm −3 , and a specific gravity of 3.15 was used in this study.The median particle size of cement was 7.55 μm, the proportion below 3 μm was 25.80%, the proportion between 3 μm to 32 μm was 69.21%, and the proportion between 32 μm to 65 μm was 4.99%.Its performance meets the requirements of GB 175-2007.

Limestone powder
The limestone powder (figure 1) with particle sizes ranging from 0 to 32 μm, a specific surface area of 2000 m 2 kg -1 , and a specific gravity of 2.65 obtained from a stone plant in the Guangdong province was used in this study.The median particle size of limestone powder was 3.01 μm, the proportion below 3 μm was 49.91%, the proportion between 3 μm to 32 μm was 50.09%.Its performance meets the requirements of GB/T 35164-2017.

Watse glass powder
The Waste glass powder (figure 2) with a specific gravity of 2.83 and a particle sizes ranging from 0 to 60 μm was obtained from a glass mill in the province of Fujian was used in this study.The median particle size of waste glass powder was 7.07 μm, the proportion below 3 μm was 29.93%, the proportion between 3 μm to 32 μm was 68.09%, and the proportion between 32 μm to 60 μm was 1.98%.Its performance meets the requirements of GB/T 51003-2014s.
The main chemical properties of cement, limestone powder and waste glass powder are shown in table 1. Particle sizes of cement, limestone powder and waste glass powder measured by laser particle size analyzer are shown in figure 3. It can be seen that the particle size of limestone powder is mainly concentrated in 0~20 μm, and the particle size distribution of waste glass powder and cement is consistent, but glass powder is finer than cement.

Other materials
Fine aggregate: the natural river sand with particle sizes ranging from 0.15 to 4.80 mm (continuous gradation), fineness modulus of 2.71 and specific gravity of 2.50 was used in this study.Coarse aggregate: the continuously graded limestone gravel with particle sizes ranging from 4.75 to 20 mm (continuous gradation), fineness modulus of 8.21, specific gravity of 2.85 was used in this study.The performance of aggregate meets the requirements of JGJ 52-2006.Water reducing agent: the polycarboxylic acid water reducing agent was used in this study, and the water reducing rate was 30%.Mixing water: in this study, laboratory tap water was used for mixing concrete.Sodium sulfate reagent: the anhydrous sodium sulfate with purity of 99% was used in this study.

Experimental procedure 3.1. Mixture proportioning
A sum of 11 experimental groups were produced, with the NC (pure cement concrete) group serving as the control group.Group L-C consisted of two types of limestone powder concrete: L10-C, which contained 10% limestone powder, and L20-C, which contained 20% limestone powder.With moderate limestone powder (suitable state), L10-C served as the control group, while with excessive limestone powder (excessive state), L20-C served as the control group.L10-W-C and L20-W-C were two series of mixed concrete containing limestone powder and waste glass powder respectively.L10-W5-C, L10-W10-C, L10-W15-C and L10-W20-C were used to study the effect of the addition of 5%, 10%, 15% and 20% waste glass powder to the mixture on the performance of the concrete based on the addition of 10% limestone powder (suitable state).L20-W5-C, L20-W10-C, L20-W15-C and L20-W20-C were used to study the effect of the addition of 5%, 10%, 15% and 20% waste glass powder to the mixture on the performance of the concrete based on the addition of 20% limestone powder (excessive state).The specimens of the aforementioned groups were cubes measuring 150 mm × 150 mm × 150 mm, with 24 specimens per group.The concrete had a design strength rating of C35, and table 2 illustrates the specific mix ratios.

Preparation of specimens
Before mixing concrete, the weighing of various materials was completed according to the mix ratio.Put coarse aggregate, fine aggregate, cement, limestone powder and waste glass powder into a mixer in turn, and then put water reducing agent into the mixing water.Finally, add water to a blender and blend for 3 min.The concrete was then injected into a mold and vibrated evenly (figure 4).After 24h of placement, the mold was removed and numbered, and the specimens were placed in a standard curing box (the temperature and relative humidity were 20 ± 2 °C and 95% respectively.)for maintenance.The preparation and curing of the specimens were carried out according to GB/T 50081-2019.

Experimental scheme
1) Mechanical property test: in accordance with GB/T 50081-2019, the compressive strength of specimens was tested 3d, 28d and 90d following the standard curing.Six specimens of each group were tested, and the average was listed.
2) Pore structure test: the compressive strength of specimens was tested 3d, 28d and 90d following the standard curing, and then crushed surface mortar blocks with aggregate removed were taken from the specimens.Hydration was stopped with anhydrous ethanol, and a MIP test was carried out after drying in an oven at 65 °C for 24h.
3) Low temperature sulfate corrosion test: in accordance with GB/T 50082-2009, the specimens were soaked in 20 ± 2 °C water for 4d following a standard curing of 24d, which were then taken out with the surface water wiped of and marked with a marker pen.Then they were put into a low temperature test chamber (figure 5) for a low temperature sulfate corrosion test (the low temperature test chamber was a freeze-thaw cycle chamber with a modified control program, which could keep the freeze-thaw solution at a low temperature of 5 °C all the time), with 5% sodium sulfate solution as the freeze-thaw solution.After soaking in low temperature sulfate solution for 180d, the specimens were taken out and their surface moisture was wiped off with a wet towel for a compressive strength test.Each group contained 6 specimens, and the results were averaged.The sulfate corrosion resistance coefficient [33] of concrete was calculated according to Formula (1): Where, K was the sulfate corrosion resistance coefficient, F 180 was the measured compressive strength of this group of specimens after soaking in low temperature sulfate solution for 180d, and F 0 was the measured compressive strength of this group of specimens after curing for 28d.4) Corrosion product test: the specimens soaked in low temperature sulfate solution for 180d were ground with damaged mortar blocks (the coarse and fine aggregates were removed) of 0 ~5 mm, 5 ~10 mm and 10 15 mm in depth, and then TG-DSC was carried out to obtain the corrosion products of specimens of different depths after a low-temperature sulfate corrosion test.Test temperature range was 25 °C ~600 °C, and the crucible was made of Al 2 O 3 , which was capped.Test atmosphere: purge gas was nitrogen, and the flow rate was 75 ml min −1 ; the protection gas was nitrogen, and the flow rate was 55 ml min −1 .

Compression strength
A compression test usually provides an overall view of the properties of concrete because strength is correlated directly to the formation of hydrated cement paste.A compression test is significant for defining the strength enhancement of the concrete specimens [34].It can be seen from figure 6 that the compressive strength of concrete of each group gradually increases with the increase of curing age.Every value is the mean of 6 specimens.When the curing age was 3d, the compressive strength of limestone powder concrete was higher than that of pure cement concrete.The compressive strength of L10-C and L20-C was 12.34% and 1.95% higher than that of NC respectively.When the curing age was 28d, the compressive strength of L10-C was higher than that of NC, while that of L20-C was lower than that of NC.The compressive strength of L10-C was 6.83% higher than that of NC, and that of L20-C was 1.64% lower than that of NC.When the curing age was 90d, the compressive strength of L10-C was still higher than that of NC, while that of L20-C was still lower than that of NC.The compressive strength of L10-C was 5.57% higher than that of NC, and that of L20-C was 4.30% lower than that of NC.The results revealed that a limestone powder dosage of 10% could improve the compressive strength of concrete, and the gain effect was more noticeable at an early curing age, but the gain effect began to fade as curing age increased.When the curing age was 3d, 20% limestone powder had gain effect on the compressive strength of concrete, but it was very weak.With the increase of curing age, it began to show deterioration effect, which is consistent with the current research results [15,20] of the academic community, according to which concrete utilizing limestone powder instead of cement mostly exhibits filling and accelerating effect.The addition of appropriate limestone powder can reduce the porosity of concrete and effectively improve its early strength.However, because limestone powder has almost no activity, secondary hydration reaction cannot occur, and an excessive addition of limestone powder is not conducive to the later hydration reaction.
It could be seen that only the compressive strength of L10-W5-C at a curing age of 3d was 1.16% higher than that of L10-C.The compressive strength of limestone powder concrete of other groups at a curing age of 3d decreased after the addition of waste glass powder.The degradation became more noticeable with more waste glass powder added.At a curing age of 28d, the waste glass powder began to show more gain effect, the compressive strength of L10-W5-C was further improved than that of L10-C, and the compressive strength of L10-W10-C was slightly higher than that of L10-C, while the deterioration of L10-W15-C and L10-W20-C was also weakened.The deterioration of waste glass powder of L20-W5-C changed to gain effect, and that of L20-W10-C, L20-W15-C and L20-W20-C was also weakened.At a curing age of 90d, the gain effect of waste glass powder of L10-W5-C and L10-W10-C was more obvious.Although the compressive strength of L10-W15-C was lower than that of L10-C, it was slightly higher than that of NC, and the deterioration effect of L10-W20-C was further weakened.The gain effect of waste glass powder of L20-W5-C was further enhanced, and the deterioration effect of that of L20-W10-C, L20-W15-C as well as L20-W20-C was further weakened.Due to the comparable pozzolanic activity of waste glass powder to fly ash, as determined through analysis, the secondary hydration reaction could be facilitated while increasing the compressive strength of concrete.However, because the secondary hydration reaction took a long time and a slow process, the influence was relatively minimal during the early stages of concrete curing.The gain effect eventually became apparent as the curing age increased.Among these, successful results were produced by adding 5% ~15% of waste glass powder to concrete that already contained 10% limestone powder.In this condition, both limestone powder and waste glass powder could increase the early strength of concrete in the middle and late phase of concrete strength respectively.The two types of gain can currently compensate for the decrease of cement material in the unit volume of concrete brought on by the decrease in cement.However, only 5% waste glass powder can be used to slightly increase the compressive strength of limestone powder concrete when it contains 20% of the material, which is because, in this case, the addition of waste glass powder would further reduce the amount of cementing material per unit volume since the limestone powder has overtaken cement.However, the strength loss brought on by the significant reduction of cementing material in the unit volume of concrete cannot be compensated by virtue of the gain effect of limestone powder or waste glass powder.As a result, the compressive strength of concrete decreased proportionately to the amount of waste glass powder added.

Pore structure
The pore structure [35,36] of concrete is an important part of its microstructure, which directly affects its mechanical properties, volume stability, permeability and long term durability.The introduction of different auxiliary cementing materials or cement substitute materials can significantly affect the pore structure of concrete due to their special physicochemical effect.Among many indexes of the pore structure of concrete, porosity [37] has the closest relationship with its mechanical properties.It can be seen from figure 7 that the porosity of concrete of each group gradually decreases with the increase of curing age.The hydration reaction of concrete is a process of continuously filling the pore structure of concrete, so its compressive strength also increases with the increase of curing age.Because the particle size of limestone powder is smaller than that of cement, it can be seen that limestone powder can be used to minimize the early porosity of concrete, while also promoting its early hydration reaction degree.However, because limestone powder limits the hydration reaction of concrete in the middle and late stages, during which the addition of limestone powder coarsened the porosity of concrete.When the dosage of limestone powder was 10%, the porosity of L10-C at each age was lower than that of NC, because its promotion effect on the early hydration of concrete exceeded its coarsening effect on the middle and late curing of concrete.However, when the dosage of limestone powder was 20%, the promotion and filling effect of limestone powder on the initial hydration of concrete was very weak due to the sharp reduction of cementing materials.At this time, the coarsening effect of limestone powder was dominant, so the porosity of L20-C was higher than that of NC at a curing age of 28d and 90d.
In the concrete mixed with 10% limestone powder and waste glass powder, only when the waste glass powder dosage was 5% did the waste glass powder have refining effect on the porosity of the concrete at a curing age of 3d.When the dosage of waste glass powder was 10% ~20%, waste glass powder mainly had coarsening effect on the porosity of concrete at a curing age of 3d.The more pronounced the coarsening effect was, the more leftover glass powder there was.Because the pozzolanic activity reaction of waste glass powder was very weak at this time, on the basis of mixing 10% limestone powder, by replacing a part of cement with waste glass powder the initial hydration reaction of concrete would be weakened.As the curing age increased, the waste glass powder began to exert its pozzolanic activity.Therefore, it could be seen that the porosity of L10-W5 and L10-W10-C on 90d was lower than that of L10-C, indicating that the promotion effect of limestone powder on the initial hydration of concrete and the pozzolanic activity of waste glass powder could make up for the decreased hydration reaction caused by the reduction of cement.On 90d, the porosity of L10-W15-C was higher than that of L10-C, but was slightly lower than that of NC, indicating that the synergistic effect of limestone powder and waste glass powder was declining.The porosity of L10-W20-C on 90d was higher than that of L10-C and NC, indicating that the coarsening effect of limestone powder and waste glass powder had been completely performed at this time.
In the concrete mixed with 20% limestone powder and waste glass powder, the waste glass powder had coarsening effect on the porosity of concrete at a curing age of 3d completely.The coarsening impact became more pronounced with more waste glass powder added, demonstrating that adding waste glass powder based on the addition of 20% limestone powder could only have coarsening effect.The pozzolanic reaction of waste glass powder increased as the curing age increased, and when the curing age reached 28d, its coarsening impact started to decline.When the curing age was 90d, the porosity of L20-W5-C was 1.58% lower than that of L20-C, indicating that waste glass powder had beneficial effect on the porosity of concrete.However, at this time, the porosity of L20-W10-C, L20-W15-C and L20-W20-C was still lower than that of L20-C, indicating that even if the pozzolanic reaction increased in the later stage of hydration, the waste glass powder still could not make up for the lack of cement hydration reaction.

Sulfate corrosion resistance
As observed in figure 8, the sulfate corrosion resistance coefficient of L10-C in the limestone powder concrete was 88.21% following the low-temperature sulfate corrosion test, which was 8.71% lower than that of NC.Following a low-temperature sulfate corrosion test, the sulfate corrosion resistance coefficient of L20-C was 69.60%, which was 22.48% less than that of NC.Taking the failure of the specimens when the sulfate corrosion resistance coefficient was lower than 75% as the criterion, L20-C had completely failed at this time.It was clear that with the addition of limestone powder, the concrete resistance to sulfate decreased, and the deterioration became more pronounced with more limestone powder added.Because with the addition of limestone powder, the alkalinity of concrete was reduced, and a lower pH value was conducive to the formation of the expandable substance gypsum, the expansion stress caused by gypsum damaged the cement structure.Gypsum also caused the decalcification of C-S-H gels, further damaging the cement structure.Moreover, limestone powder could provide carbonate ions needed by the formation of carbonite [17].Concrete mixed with limestone powder was prone to producing TSA failure under long-term sulfate attack at a low temperature (<15 °C) [15,16].The excessive addition of limestone powder would worsen the aforementioned chemical level while reducing the amount of cementitious materials per unit volume, coarsening the concrete aperture and making it more conductive to the invasion of corrosive substances.As a result, the sulfate corrosion resistance of L20-C was reduced more than that of L10-C.
In the concrete mixed with 10% limestone powder and waste glass powder, after a low temperature sulfate corrosion test, the sulfate corrosion resistance coefficient of L10-W5-C was 88.21%, which was 4.84% higher than that of L10-C but 3.87% lower than that of NC.The sulfate corrosion resistance coefficient of L10-W10-C was 90.03%, which was 6.66% higher than that of L10-C but 2.05% lower than that of NC.The sulfate corrosion resistance coefficient of L10-W15-C was 84.12%, which was 0.75% higher than that of L10-C but 7.96% lower than that of NC.The sulfate corrosion resistance coefficient of L10-W20-C was 80.94%, which was 2.43% and 11.14% lower than that of L10-C and NC respectively.It could be seen that the sulfate corrosion resistance of limestone concrete could be improved by adding 5% ~15% waste glass powder on the basis of 10% limestone powder, and the best effect was achieved when the waste glass powder dosage was 10%, and the sulfate corrosion resistance of L10-W10-C was very close to that of NC (the sulfate corrosion resistance of concrete at this time was about 97.77% of that of pure cement concrete).When the dosage of waste glass powder exceeded 15%, the sulfate corrosion resistance of limestone concrete decreased.According to an analysis, on the one hand, waste glass powder has pozzolanic activity, which can consume CH (Calcium hydroxide) and reduce the sulfate corrosion degree; on the other hand, with the pozzolanic activity of waste glass powder, C-S-H gels can be continuously generated, making the concrete maintain a high compressive strength growth rate after curing for 28d, which is conducive to resisting the invasion of sulfate ions [38,39].Therefore, limestone powder and waste glass powder showed synergistic action in L10-W5-C, L10-W10-C and L10-W15-C, whose sulfate corrosion resistance was improved compared to L10-C.Mahdi et al also found that the concrete mixture containing 15% waste glass powder showed excellent performance against sulfuric acid attack [40].However, when the dosage of waste glass powder exceeded 15%, limestone powder and waste glass powder replaced more than 25% of the cement.The filling effect of limestone powder or the pozzolanic activity of waste glass powder was not enough to make up for the decrease of concrete compressive strength or pore coarsening caused by the substantial reduction of cementing material in unit volume.Therefore, the sulfate corrosion resistance of L10-W20-C further decreased compared with that of L10-C.
In the concrete mixed with 20% limestone powder and waste glass powder, after a low temperature sulfate attack test, the sulfate corrosion resistance coefficient of L20-W5-C was 76.12%, which was 6.52% higher than that of L20-C but 15.96%% lower than that of NC.The sulfate corrosion resistance coefficient of L20-W10-C was 71.22%, which was 1.62% higher than that of L20-C but 20.86%% lower than that of NC.The sulfate corrosion resistance coefficient of L20-W15-C was 67.86%, which was 1.74% and 24.22% lower than that of L20-C and NC respectively.The sulfate corrosion resistance coefficient of L20-W20-C was 64.90%, which was 4.70% and 27.18% lower than that of L20-C and NC respectively.It could be seen that on the basis of adding 20% limestone powder, the sulfate corrosion resistance of limestone powder concrete could be improved when the content of waste glass powder was 5% ~10%, and there was the best effect when the dosage of waste glass powder was 5%.When the dosage of waste glass powder was higher than 10%, the sulfate corrosion resistance of limestone powder concrete was deteriorated.The higher the content of waste glass was, the more obvious the deterioration effect would be, indicating that the pozzolanic activity of waste glass powder was not enough to make up for the coarsening of pore size caused by the reduction of cementing material in unit volume.At the same time, because the absorption ratio of waste glass powder was almost zero [41], excessive glass powder would make the actual water-cement ratio of concrete increase, which was not conducive to the sulfate corrosion resistance of concrete.

Corrosion products
In the low temperature sulfate corrosion test, sulfate ions were mixed into the concrete.On the one hand, AFt (ettringite) was produced using cement stone CH and calcium aluminate hydrate reaction, causing an internal stress; on the other hand, it reacted with the CH in the cement stone to form the expansive material gypsum, which caused an expansion stress.TG-DSC can be used to obtain mass changes and heat absorption while releasing changes synchronously using the same samples of the same measurement.The phases of interest are the C-S-H gels and corrosion products of gypsum, AFt and CH.Studies [42,43] show that C-S-H gels decompose at 90 ~110 °C, gypsum and AFt decompose at 130 ~150 °C, and CH decomposes at 400 ~450 °C.The specimens after the low-temperature sulfate corrosion test were ground with damaged mortar blocks of 0 5 mm, 5 ~10 mm and 10 ~15 mm in depth, and then TG-DSC was carried out to obtain the corrosion products.The TG-DSC analyses of concrete following the low-temperature sulfate corrosion test are shown in figures 9-19.The mass change rate of concrete after the test is shown in figures 20-22.
In the limestone powder concrete, the content of AFt/gypsum in L10-C was slightly higher than that in NC at the depth of 0 ~5 mm and 5 ~10 mm; while at the depth of 10 ~15 mm, its content was slightly lower than that of NC.This indicated that although 10% limestone powder had degraded the sulfate corrosion resistance of concrete at the chemical level, it had little influence on the sulfate corrosion resistance of concrete in the deep layer because limestone powder showed good filling effect and improved the density of concrete.The AFt/ gypsum content of L20-C at 0 ~5 mm, 5 ~10 mm and 10 ~15 mm was significantly higher than that of NC.Meanwhile, we should note that the C-S-H gel content of L20-C at 0 ~5 mm, 5 ~10 mm and 10 ~15 mm was significantly lower than that of NC, which showed that the excessive incorporation of limestone powder, on the one hand, caused the increase of sulfate corrosion products; on the other hand, the excess replacement of cement by limestone powder resulted in the reduction of cementing material per unit volume, which inhibited the later hydration of concrete and led to the increase of corrosion depth.
In the concrete mixed with 10% limestone powder and waste glass powder, the AFt/gypsum content of L10-W5-C was higher than that of NC but lower than that of L10-C at the depth of 0 ~5 mm, 5 ~10 mm and 10 15 mm.The C-S-H gel content of L10-W5-C at 0 ~5 mm, 5 ~10 mm and 10 ~15 mm was higher than that of L10-C and NC.The AFt/gypsum content of L10-W10-C was further reduced at the depth of 0 ~5 mm, 5 10 mm and 10 ~15 mm.The C-S-H gel content of L10-W10-C further increased at the depth of 0 ~5 mm, 5 10 mm and 10 ~15 mm.The AFt/gypsum content of in L10-W15-C at 0 ~5 mm, 5 ~10 mm and 10 ~15 mm increased, but was lower than that of L10-C; the C-S-H gel content of L10-W15-C at the depth of 0 ~5 mm, 5 10 mm and 10 ~15 mm decreased compared with that of L10-C.The content of AFt/gypsum in L10-W20-C at 0 ~5 mm, 5 ~10 mm and 10 ~15 mm increased, but was lower than that of L10-C; the C-S-H gel content of L10-W15-C at the depth of 0 ~5 mm, 5 ~10 mm and 10 ~15 mm further decreased compared with that of L10-C.The above indicated that the addition of waste glass powder could exert its pozzolanic activity, consume part of CH, reduce the sulfate reaction degree of limestone powder concrete, and reduce the production of sulfate attack products.On the other hand, the pozzolanic activity of waste glass powder could improve the problem that limestone powder inhibited the hydration of concrete in later stages.However, the excessive incorporation of waste glass powder would lead to the reduction of cementing material in the unit volume of concrete, resulting in the reduction of C-S-H gels, which had adverse effects on the sulfate corrosion resistance of concrete.
In the concrete mixed with 20% limestone powder and waste glass powder, the AFt/gypsum content of L20-W5-C and L20-W10-C at the depth of 0 ~5 mm, 5 ~10 mm and 10 ~15 mm was lower than that of L20-C.The content of AFt/gypsum in L20-W15-C and L20-W20-C at the depth of 0 ~5 mm, 5 ~10 mm and 10 ~15 mm was higher than that in L20-C.It was worth noting that the C-S-H gel content of L20-W5-C was slightly higher than that of L20-C at the depth of 0 ~5 mm, 5 ~10 mm and 10 ~15 mm, while that of L20-W10-C, L20-W15-C and L20-W10-C was lower than that of L20-C at 0 ~5 mm, 5 ~10 mm and 10 ~15 mm.The higher the dosage of waste glass powder was, the lower the C-S-H gel content was, indicating that in the concrete mixed with 20% limestone powder, because limestone powder had replaced a large part of cement, the improvement effect of waste glass powder on the sulfate corrosion resistance of concrete was very weak.With the increase of waste glass powder dosage, more coarsening effect was shown.The decrease of C-S-H gel content led to a further decrease in the sulfate corrosion resistance of concrete.

Conclusion
In this paper, limestone powder and waste glass powder were mixed to replace part of cement to produce concrete.The evolution law of compressive strength, porosity, sulfate corrosion resistance and corrosion of limestone powder and waste glass powder mixed concrete products of different proportions was studied.Based on the results presented, the following conclusions can be drawn: (1) The early strength of concrete could not be improved by adding waste glass powder, but its late strength could be improved.In the concrete mixed with 10% limestone powder, the compressive strength was improved by mixing 5% ~10% waste glass powder, but it was deteriorated by mixing 15% ~20% waste glass powder.The compressive strength of concrete mixed with 20% limestone powder could be improved slightly with only 5% waste glass powder, while 10% ~20% waste glass powder could degrade its compressive strength.(2) The variation regularity of concrete porosity was consistent with that of its compressive strength.In the concrete mixed with 10% limestone powder, 5% ~10% waste glass powder reduced the porosity, but 15% 20% waste glass powder played a coarsening role.In the concrete mixed with 20% limestone powder, the porosity was slightly reduced with only 5% waste glass powder, and the coarsening effect occurred when mixing 10% ~20% waste glass powder.
(3) The sulfate corrosion resistance of limestone powder concrete could be improved by adding 5% ~15% waste glass powder into the concrete mixed with 10% limestone powder, and the best effect was achieved when the waste glass powder content was 10% (the sulfate corrosion resistance of concrete at this time was about 97.77% of that of pure cement concrete).In the concrete with 20% limestone powder, the sulfate corrosion resistance of limestone powder could be improved when the dosage of waste glass powder was 5% ~10%, and there was the best effect when the dosage of waste glass powder was 5%.
(4) The corrosion products showed that its pozzolanic activity could be exerted with the addition of waste glass powder, consuming part of CH, meanwhile reducing the sulfate reaction degree of limestone powder concrete and the production of corrosion products.In addition, the pozzolanic activity of waste glass powder could improve the problem that limestone powder inhibited the hydration of concrete in later stages.However, the excessive incorporation of waste glass powder would lead to the reduction of cementing material in the unit volume of concrete, resulting in the reduction of C-S-H gels, which had adverse effects on the sulfate corrosion resistance of concrete.
Later research can be carried out in the following directions.The first is to make use of existing advanced mix design methods, such as a dynamic hydration model, to more accurately study the optimal mix ratio of limestone powder and waste glass powder.The second is to study the other properties of limestone powder and waste glass powder mixed concrete, such as shrinkage cracking, chloride ion resistance and carbonization resistance, etc In addition, the laboratory test conditions are relatively ideal.Therefore, the mechanism by which the physical and chemical properties of limestone powder and waste glass powder from different sources affect the performance of concrete should be given attention and studied.Ultimately, establish a universal standard for the mixed use of limestone powder and waste glass powder.

Figure 3 .
Figure 3. Particle size distribution of Cement, Waste glass powder and Limestone powder.

Figure 6 .
Figure 6.Compressive strength of concrete at different curing ages.

Figure 7 .
Figure 7. Porosity of concrete at different curing ages.

Figure 9 .
Figure 9. TG-DSC analyses of NC following low temperature sulfate corrosion test.

Figure 10 .
Figure 10.TG-DSC analyses of L10-C following low temperature sulfate corrosion test.

Figure 15 .
Figure 15.TG-DSC analyses of L20-C following low temperature sulfate corrosion test.

Figure 20 .
Figure 20.Mass change rate(C-S-H) of concrete after low temperature sulfate corrosion test.

Figure 21 .
Figure 21.Mass change rate (AFt/Gypsum) of concrete after low temperature sulfate corrosion test.

Table 1 .
Main chemical properties of cement, limestone powder and waste glass powder (%).