Influence of Dolomite Rock Powder and Iron Tailings Powder on the Electrical Resistivity, Strength and Microstructure of Cement Pastes and Concrete

Abstract

Dolomite rock powder (the waste stone residue in the production of machine-made sand and stone processing) and iron tailings powder formed by mineral processing industry are solid wastes, which occupy land resources, pollute the environment and release toxic substances without reasonable processing. The dolomite rock powder and iron tailings powder composing a large number of active substances could be advantageous to the cement-based materials. In this study, the electrical resistivity of cement paste and concrete was measured. Meanwhile, the influence of dolomite rock powder and iron tailings powder on the compressive strength of concrete was investigated. The electric flux of concrete was determined to estimate the chloride ion permeability. The scanning electron microscope (SEM) and X-ray diffraction were obtained to investigate the hydration of cement paste. Results showed the electrical resistivity of all specimens presented in this order: specimens with iron tailings < specimens with dolomite rock powder < blank specimens < specimens with ground granulated blast-furnace slag (GGBS) < specimens with fly ash. The correlation between electrical resistivity and curing age of cement paste or concrete has been deduced as a quadratic function. The addition of GGBS could improve the compressive strength of concrete. Meanwhile, when the other three types of mineral admixtures were added, 5% by mass ratio of the total binder materials was the optimum for the compressive strength. The curing ages, the fly ash, the GGBS and 5% dolomite rock powder or 5% iron tailings powder demonstrated a positive effect on the chloride ion impermeability. However, when higher dosages of dolomite rock powder or iron tailings powder were added, the effect was the opposite. Finally, the compactness of the microstructure and the Ca(OH)₂ of cement paste could be improved by a small dosage of dolomites or iron tailings (less than 5%).

1. Introduction

Concrete is an important human-made civil engineering material, which has been widely used for many years [1,2,3]. With the rapid development of housing construction, a large amount of solid waste formed. The accumulation of solid waste without reasonable treatment will not only pollute the environment, but also affect the appearance of the city [4]. The recycling of solid waste in building materials provides an innovative idea for the treatment of solid waste [5,6].

Researchers found that the solid wastes like waste fly ash and rice husk ash possessing active substances could promote the hydration process of cement. The addition of waste fly ash and rice husk ash were proven to increase the mechanical strengths and durability of concrete [7,8,9]. Moreover, the waste fly ash and rice husk ash could improve the corrosion resistance of steel bars in the reactive powder concrete. The main problem with fly ash is that, as we increase the quantity, the hydration reaction is slowed down and the rate of strength gain is reduced. A number of scientists are adding nanoparticles to mitigate this [10,11]. Meanwhile, the rice husk ash is produced by burning rice husk. A large amount of carbon dioxide gas will be produced during the production [12,13]. Additionally, commonly used mineral admixtures are in short supply, thus the prices are rising with time. Summarily, other reasonable solid wastes or resources need to be excavated and applied to concrete.

Dolomite rock powder and iron tailings powder are produced by the sand gravel processing industry and metallurgical industry [14]. The accumulation of dolomite rock powder induces the occupation of land. Additionally, the iron tailings powder can pollute the environment and release toxic substances without reasonable processing. Therefore, the treatment and comprehensive utilization of stone powder and iron tailings have become an urgent problem to be solved [14,15]. Previous studies pointed out that the addition of an appropriate amount of dolomite rock powder can improve the micropores of concrete and improve the mechanical properties, carbonation and frost resistance of concrete [16,17]. Moreover, the iron tailings have good grindability and a low price. It is technically feasible to use iron tailings powder as concrete mineral admixture [18,19]. Lu et al. [20] found that adding iron tailings powder to cement can improve the compressive strength of concrete. Song Shaomin et al. [21] discovered that adding an appropriate amount of iron tailings powder can improve the chloride ion permeability and carbonation resistance of concrete. The electrical resistivity of cement-based materials can be used to reflect the hydration process of cement and the corrosion resistance of steel bars inner concrete [22,23,24,25]. However, little attention was paid to the electrical resistivity of cement-based materials with dolomite rock powder and iron tailings powder. Moreover, the influence of dolomite rock powder and iron tailings powder on the mechanical performance, the electrical property and microscopic mechanism should be studied systematically.

In this study, the electrical resistivity of cement paste or concrete with iron tailings, dolomite rock powder, ground granulated blast-furnace slag and fly ash was studied. Moreover, the following compressive strength and chloride ion permeability were determined. The curing age ranged from 3 days to 210 days. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were obtained for the mechanism analysis of the properties. This research will provide a basis for the application of these two solid wastes in construction building materials in the future.

2. Experimental Section

2.1. Raw Materials

The fly ash (FA) was provided by Beijing Jing Ye Da New Building Materials Co., Ltd., Beijing, China, showing the air drying water content of 1.5%, the specific surface area of 385 m²/kg and the maximum dry density of 2.21 g/cm³. Granulated blast furnace slag powder (GGBS) with a density of 2.85 g/cm³, a specific surface area of 450 m²/g and a loss on ignition of 2.1% produced by Hebei Jintaicheng Environmental Resources Co., Ltd., Xingtai, China, was applied in the experiments. Ordinary Portland cement manufactured by Beijing Jinyu Group Co., Ltd., Beijing, China, was used in the study. The strength grade of ordinary Portland cement is 42.5 MPa. The micro powder of iron tailings was produced by Fujian Quanzhou Meiling Group Co., Ltd., Quanzhou, China, was used for manufacturing the specimens. The micro-powder of iron tailings showed a density of 3.125 g/cm³ and a specific surface area of 517 m²/kg. The dolomite rock powder was provided by Beijing high strength Concrete Co., Ltd., Beijing, China, showing a density of 2.73 g/cm³ and a specific surface area of 200 m²/kg.

The natural river sand with a fineness modulus of 2.9 manufactured by Beijing Yugou Co., Ltd., Beijing, China, was used as fine aggregate in this study. The sand belonging to the medium sand possesses the apparent density of 2677 kg/m³ and bulk density of 1546 kg/m³. The coarse aggregate used for manufacturing concrete was the crushed limestone produced by Beijing Yugou Precast Concrete Engineering, Beijing, China. The coarse aggregate with the particle sizes of 5–10 mm and 10–20 mm and the following mass ratios of 30% and 70% were used in this study. Meanwhile, the crushing index, the apparent density and the bulk density of crushed limestone were 5.2%, 2800 kg/m³ and 1650 kg/m³, respectively. The total mud content of all aggregates was 1.3%. The particle size distributions and chemical compositions are shown in

Table 1. Particle passing percentage of the cementitious materials/%.

Types	Particle Size/μm
	0.3	0.6	1	4	8	64	360	580
Cement	0.1	1.35	3.68	23.79	39.46	94.12	100	100
Fly ash	0.49	1.54	2.93	19.54	37.9	92.99	100	100
GGBS	0.31	1.78	4.2	21.85	38.68	100	100	100
Dolomite	0	0.58	1.45	7.14	13.01	75.91	97.41	100
Iron tailings	0.21	2.28	6.55	32.22	47.91	100	100	100

and

Table 2. Chemical composition of the cementitious materials/%.

Types	CaO	SiO2	Al2O3	Fe2O3	MgO	SO3	K2O	MnO	Loss
Cement	4.55	50.23	33.22	5.95	0.79	0.91	1.48	/	2.81
Fly ash	4.55	50.23	33.22	5.95	0.79	0.91	1.48	/	2.81
GGBS	42.19	27.56	15.80	0.31	7.52	2.89	0.45	/	1.89
Dolomite	48.62	29.67	0.72	0.47	20.17	0.05	0.18	/	0.07
Iron tailings	14.78	47.35	5.05	23.56	1.55	2.04	/	3.21	2.46

, respectively.

2.2. Characterization Methods

2.2.1. Samples Preparation

The preparation of all specimens was carried according to the mixing proportions of

Table 3. Mix proportion of the cement paste or concrete/kg/m³.

Cement	Fine Aggregate	Coarse Aggregate	Fly Ash	GGBS	Dolomites	Iron Tailings	Water
457	-	-	-	-	-	-	146
434.2	-	-	22.8	-	-	-	146
411.3	-	-	45.7	-	-	-	146
388.5	-	-	68.5	-	-	-	146
434.2	-	-	-	22.8	-	-	146
411.3	-	-	-	45.7	-	-	146
388.5	-	-	-	68.5	-	-	146
434.2	-	-	-	-	22.8	-	146
411.3	-	-	-	-	45.7	-	146
388.5	-	-	-	-	68.5	-	146
434.2	-	-	-	-	-	22.8	146
411.3	-	-	-	-	-	45.7	146
388.5	-	-	-	-	-	68.5	146
457	753	1080	-	-	-	-	160
434.2	753	1080	22.8	-	-	-	160
411.3	753	1080	45.7	-	-	-	160
388.5	753	1080	68.5	-	-	-	160
434.2	753	1080	-	22.8	-	-	160
411.3	753	1080	-	45.7	-	-	160
388.5	753	1080	-	68.5	-	-	160
434.2	753	1080	-	-	22.8	-	160
411.3	753	1080	-	-	45.7	-	160
388.5	753	1080	-	-	68.5	-	160
434.2	753	1080	-	-	-	22.8	160
411.3	753	1080	-	-	-	45.7	160
388.5	753	1080	-	-	-	68.5	160

. The samples of cement paste were manufactured following these steps:

In order to prepare the cement paste, the NJ-160A cement paste mixer offered by Hebei Yuhong Instrument Equipment Co., Ltd., Cangzhou, China, was used. Firstly, the cementitious materials were added to the mixer and mixed at the mixing speed of 62 r/min for 1 min. Then, the mixture of water reducer and water was added and mixed at this speed for another 1 min. Finally, all mixtures were mixed at the speed of 140 r/min for the last two minutes. The fresh cement paste was poured into the molds for manufacturing the specimens of size of 40 mm × 40 mm × 160 mm. The specimens were demolded after cured in the environment with a temperature of 20 ± 2 °C and the relative humidity of 40% for 1 d.

For manufacturing the concrete specimens, all cementitious materials and aggregates were added to the SJD-60 single horizontal shaft concrete mixer manufactured by Cangzhou tiantuo Instrument Equipment Co., Ltd., Cangzhou, China and mixed at the speed of 48 r/min for 4 min. In this study, six specimens were selected for each experiment. The average value and error bar of each parameter were used for evaluating the properties of specimens.

2.2.2. Measurement of Electrical Resistivity

The electrical resistance of specimens was measured after cured in standard curing environment (20 ± 2 °C and relative humidity of above 95%) for 3 d, 7 d, 14 d, 28 d, 56 d, 180 d and 210 d. A 16-mesh copper mesh produced by Hebei Haiji Wire Mesh Co., Ltd., Hengshui, China, was used for the test of electrical resistance. The electrical resistivity can be calculated by Equation (1) [26].

$$\rho =\frac{RS}{L}$$

(1)

Where R means the electrical resistance of specimen, S is the interface area of specimen and L is the length of specimen.

Specimens with sizes of 40 mm × 40 mm × 160 mm and 100 mm × 100 mm × 300 mm were used for the determination of electrical resistance of cement paste and concrete, respectively. The electrode sizes for the determination of electrical resistance of cement paste and concrete were 30 mm × 50 mm and 70 mm × 110 mm. The spacing between two electrodes of cement paste and concrete were 120 and 200 mm, respectively. The voltammetry was selected for the measurement of electrical resistance. Voltmeter and ammeter of specimens were collected with Victor 8246 desktop multimeter produced by Xi’an Shengli Instrument Co., Ltd., Xi’an, China. The electrical signal generator was DG822 function/arbitrary waveform generator produced by Puyuan Jingdian Technology Co., Ltd., Suzhou, China. The measurement of electrical resistance was shown in Figure 1.

2.2.3. Measurement of Compressive Strength and Chloride Ion Permeability

Concrete specimens with sizes of 100 mm × 100 mm × 100 mm and Φ 100 mm × 50 mm were used for the measurement of compressive strength and chloride ion permeability parameters. The compressive strength of concrete was determined by Yaw-3000 microcomputer controlled electro-hydraulic servo pressure testing machine produced by Shanghai Sansi Zongheng Machinery Manufacturing Co., Ltd., Shanghai, China. Compressive strength was conducted according to Chinese standard GB/T 50081-2019 [27]. The loading rate for the compressive strength of concrete was 0.5 MPa/s. For determining the chloride ion permeability parameters, the electric flux method was applied. Before the measurement, the specimens were soaked in the NEL-VJH type concrete vacuum machine manufactured by Beijing Nile instrument and Equipment Co., Ltd., Shanghai, China for 48 h. After this step, the water saturated specimens were moved to the NEL-PDU type chloride diffusivity tester provided by Beijing Nile instrument and Equipment Co., Ltd., Shanghai, China. The NaCl solution with concentration of 3% and the NaOH solution with concentration of 0.3 mol/L were applied in the cathode and anode, respectively. The experiment of chloride ion permeability parameters was carried out according to the Chinese Standard GB/T 50082-2009 [28].

2.2.4. Experiments of SEM and XRD

The process of SEM and XRD experiments can be described as follows:

The soybean size of hardened cement paste was taken from the inner specimens cured in the standard curing environment for 28 days, meanwhile, some other sample was ground into powder. The selected samples were immersed in the absolute ethanol for 4 days to prevent the hydration of cement. After that, all samples were dried in the vacuum drying oven produced by Shanghai Hecheng Instrument Manufacturing Co., Ltd., Shanghai, China at the temperature of 60 °C for 4 days. The dried samples were sprayed by gold before measurement. After these steps were finished, the SEM (Hitachi Limited., Tokyo, Japan) experiment was carried out. The ground powder of specimen was moved to the D8 ADVANCE X-ray diffractometer (Bruker Corp., Tokyo, Japan) for the measurement of the XRD.

3. Results and Discussion

3.1. Electrical Resistivity

Usually, the blank concrete cannot be used in the practical projects [29]. As described in some journals, the electrical resistivity can be used for the reflection of corrosion resistance of the inner metal materials of concrete [30]. Electrons from metallic materials in concrete can be difficult to move when the electrical resistivity of concrete was higher thus showing better corrosion resistance [31]. In this study, the electrical resistivity of cement-based materials was determined to reflect the corrosion resistance of inner metal reinforced materials. Figure 2 shows the electrical resistivity of cement paste and concrete with fly ash, GGBS, dolomites and iron tailings. As shown in Figure 2, the electrical resistivity increased in the form of quadratic function with the increasing curing age, due to the fact that the electrical resistivity of cement paste and concrete was dominated by the free ions of the pore solution [32,33]. The free water was decreased with the increasing curing ages due to the process in hydration thus reducing the free ions and the electrical conduction [34]. Therefore, the electrical resistivity increased with the curing age. Moreover, it could be observed from Figure 2, the addition of fly ash and GGBS led to increasing the electrical resistivity of cement paste and concrete. However, when the dolomites or iron tailings were added to the cement paste or concrete, the results were the opposite. This was attributed to the fact that the additions of mineral admixtures could accelerate the hydration process of cement thus decreasing the free water inner cement-based materials leading eventually to increasing the electrical resistivity of cement paste or concrete [35]. However, the dolomites and iron tailings possessing large amount of metal elements resulted in increasing free electrons of cement-based materials thus improving the electrical conduction and decreasing the following electrical resistivity [36]. The electrical resistivity of cement paste or concrete with fly ash was the highest, for the metallic elements of fly ash were the lowest.

Table 4. The fitting results between the electrical resistivity and mass ratios of mineral admixtures.

Mineral Admixtures	Types	Content/%	a	b	c	R2
Fly ash	Cement paste	0	−2.6 × 10−4	0.14	8.78	0.968
		5	−3.0 × 10−5	0.22	7.73	0.998
		10	3.0 × 10−5	0.24	7.52	0.999
		15	5.0 × 10−5	0.27	7.31	0.998
	Concrete	0	−5.3 × 10−4	0.64	26.27	0.997
		5	−1.0 × 10−4	0.99	24.13	0.998
		10	−2.1 × 10−4	1.27	21.81	0.999
		15	−2.7 × 10−3	1.49	20.28	0.999
Slag	Cement paste	0	−2.6 × 10−4	0.14	8.78	0.968
		5	−6.0 × 10−4	0.24	9.87	0.911
		10	−9.4 × 10−4	0.31	10.75	0.869
		15	−1.0 × 10−3	0.35	11.63	0.860
	Concrete	0	−5.3 × 10−4	0.64	26.27	0.997
		5	6.3 × 10−4	0.48	31.03	0.981
		10	−1.5 × 10−4	0.94	33.03	0.967
		15	−3.0 × 10−3	1.35	34.46	0.938
Dolomite rock powder	Cement paste	0	−2.6 × 10−4	0.14	8.78	0.968
		5	−1.1 × 10−4	0.11	8.02	0.973
		10	−1.5 × 10−4	0.11	7.80	0.981
		15	−2.1 × 10−4	0.12	7.68	0.987
	Concrete	0	−5.3 × 10−4	0.64	26.27	0.997
		5	−5.2 × 10−3	1.57	31.57	0.925
		10	−4.5 × 10−3	1.42	27.06	0.939
		15	−2.7 × 10−3	0.99	38.15	0.953
Iron tailings	Cement paste	0	−2.6 × 10−4	0.14	8.78	0.968
		5	−1.5 × 10−4	0.09	8.45	0.973
		10	−3.9 × 10−4	0.14	6.91	0.992
		15	−2.9 × 10−4	0.12	6.31	0.985
	Concrete	0	−5.3 × 10−4	0.64	26.27	0.997
		5	−3.0 × 10−3	1.03	37.61	0.943
		10	−2.2 × 10−3	0.86	34.69	0.965
		15	−2.0 × 10−3	0.79	29.16	0.972

shows the fitting results of the relationship between the electrical resistivity and the curing age. The fitting equation can be described in Equation (2). It can be depicted that, the fitting equations of electrical resistivity and the curing ages fits with quadratic function. As obtained from Table 4, the fitting degrees of all curves were higher than 0.86, indicating that the fitting equation is reasonable.

$$\rho =\mathrm{a}{t}^2+bt+c$$

(2)

where a, b and c are constants of the fitting equations, t is the curing age.

3.2. The Compressive Strength and Chloride Ion Permeability

Figure 3 shows the compressive strength of concrete with different types and dosages of mineral admixtures. As depicted in Figure 3, the compressive strength of concrete decreased with the increasing dosages of fly ash, due to the fact that the existing defects in fly ash thus decreasing the compressive strength of concrete [37,38]. Moreover, when GGBS was added to the concrete, the compressive strength increased. This was attributed to the fact that the GGBS possessed large amount of CaO, Si₂O and Al₂O₃, leading eventually to accelerating hydration process of the concrete forming hydrated calcium silicate and hydrated calcium aluminate [39]. Therefore, the compressive strength of concrete was improved by the addition of GGBS. Furthermore, the compressive strength of concrete firstly increased and then decreased with the increasing dosages of dolomites and iron tailings. This was attributed to the fact that the filling effect of dolomites and iron tailings could improve the compactness of concrete, thus increasing the compressive strength of the concrete [40,41]. Moreover, the active substances of dolomites and iron tailings could promote the hydration of cement, thus improving the compressive strength [42]. However, the internal defects of dolomites and iron tailings could result in the decrease of the compressive strength [43,44].

Figure 4 shows the electric flux of concrete with different types and dosages of mineral additives. As observed from Figure 4, the electric flux of concrete decreased with the increasing curing age, indicating the decline in the chloride ion permeability of concrete. This was attributed to the fact that the increasing curing age led to the further development of hydration, thus improving the compactness of the internal structures of concrete and then decreasing the chloride ion permeability [45]. The electric flux of concrete decreased with the increasing dosages of fly ash and GGBS. However, when the dolomite rock powder and iron tailings were added, the electric flux of concrete firstly decreased and then increased with their increasing dosages. This signifies that the resistance of chloride ion permeability of concrete firstly increased and then decreased with the increasing dosages of dolomite rock powder and iron tailings [19,21,46].

Figure 5 shows the relationship between the electric flux and electrical resistivity of concrete with different types and dosages of mineral admixures. As illustrated in Figure 5, the electric flux decreased in the form of quadratic function just expressed in Equation (3).

Table 5. The fitting results between electric flux and electrical resistivity of concrete.

Types	M/%	a	b	R2
Fly ash	0	1.5 × 105	−1.09	0.931
	5	1.8 × 105	−1.09	0.939
	10	6.5 × 105	−1.37	0.956
	15	2.6 × 106	−1.67	0.960
GGBS	0	1.5 × 105	−1.09	0.931
	5	1.5 × 105	−1.08	0.867
	10	5.1 × 105	−1.32	0.859
	15	1.52 × 105	−1.51	0.847
Dolomite rock powder	0	1.5 × 105	−1.09	0.931
	5	6.7 × 106	−1.87	0.862
	10	1.04 × 105	−1.42	0.900
	15	1.7 × 105	−1.01	0.999
Iron tailings	0	1.5 × 105	−1.09	0.931
	5	7.0 × 106	−1.87	0.900
	10	1.8 × 106	−1.59	0.960
	15	6.6 × 105	−1.39	0.930

shows the fitting results. The fitting degrees of all curves were higher than 0.847, indicating the rationality of the fitting functions.

$$E_f=a{\rho }^b$$

(3)

where a and b constants of the fitting equations, E_f is the electric flux and ρ is electrical resistivity.

3.3. SEM and XRD Analysis

The scanning electron microscope (SEM) was observed to investigate the effects of dolomite and iron tailings on the microstructures of cement paste. The samples for the determination of scanning electron microscope were firstly dried in the vacuum drying oven produced by Shanghai Hecheng Instrument Manufacturing Co., Ltd., Shanghai, China at the temperature of 60 °C for 4 days. The dried samples were sprayed by gold before measurement. After the steps were finished, the SEM experiment was carried out. Figure 6 shows the SEM result of cement paste with different dosages of dolomites and iron tailings. As shown in this figure, the needle-like hydration products exist in the blank specimen. When 5% dolomite was added in the cement paste, the hydration products were more compact. However, when the dosage of dolomite was 15%, more unhydrated particles could be found in the microstructure. Therefore, the compressive strength of concrete increased with the dosages of dolomites increasing from 0% to 5% and decreased with the dolomite increasing from 5% to 15%. Moreover, when the content of iron tailings was 5%, the hydration products were larger and more compact, thus improving the compressive strength of concrete. However, when the addition of iron tailings was 15%, more pores were observed in the cement paste, thus confirming that the compressive strength was reduced when the content of iron tailings was 15%.

Figure 7 shows the X-ray diffraction (XRD) pattern photos of specimens containing different dosages of iron tailings and dolomite rock powder. The XRD experiment was carried out after the dried samples were ground into powder. It can be observed from Figure 7 that all the spectra show strong diffraction peaks of 3CaO·SiO₂ (C₃S), 2CaO·SiO₂ (C₂S), cristobalite (SiO₂), Ca(OH)₂ and CaCO₃. Moreover, as shown in Figure 7, the height of diffraction peak of Ca(OH)₂ increased with the addition of iron tailings increasing from 0% to 5%. However, when the addition of iron tailings increased from 5% to 15%, the diffraction peak of Ca(OH)₂ decreased. This was attributed to the fact that the active substances of iron tailings could improve the hydration of cement, thus consuming the Ca(OH)₂ [18]. However, when the content of iron tailings increased from 5% to 15%, the hydration of cement was insufficient, leading to increasing the content of Ca(OH)₂, therefore the diffraction peak of Ca(OH)₂ increased [47]. Furthermore, the increasing content of dolomite rock powder led to increasing the diffraction peak of Ca(OH)₂ due to the fact that dolomite rock powder consisted of a large amount of CaO, the CaO reacted with water and formed Ca(OH)₂, thus increasing the diffraction peak of Ca(OH)₂.

4. Conclusions

In this study, the electrical and mechanical properties of cement paste and concrete with iron tailings and dolomite rock powder were studied. The results provide guidelines for the application of these two solid wastes in construction materials. The following conclusions can be summarized:

(1)

The corrosion resistances of cement-based materials with different additives were determined by the electrical resistivity tests. The electrical resistivity of cement-based materials increases as a function of curing age, indicating the gradual solidification of free ions in cement over time. However, the electrical resistivity changes are highly sensitive to the chemical composition of additives.

(2)

The addition of ground granulated blast-furnace slag can improve the compressive strength of concrete, however, fly ash will play an opposite effect. Additionally, the compressive strength of concrete exhibits an increase and then decrease trend with the increase of dolomites and iron tailings.

(3)

The impermeability of chloride ions in concrete exhibits the first increase and then decrease trend with the increasing dosages of dolomite rock powder and iron tailings through the electric flux method.

(4)

The microstructure of cement pastes can be compacted when adding a small dosage of dolomites or iron tailings (less than 5%) due to the hydration promotion effect of additives. However, the microstructure of cement paste exhibits a deterioration with an excess content of dolomites or iron tailings, which is attributed to the internal defects of additives.