Influence of Molybdenum Tailings Sand Substitution Amount on Mechanical Properties and Microstructure of Manufactured Sand Cement Mortar

doi:10.16552/j.cnki.issn1001-1625.2025.0708

Abstract

Abstract:

To alleviate the shortage of sand resources and achieve resource utilization of industrial solid waste， this study investigated the effect of substituting manufactured sand with molybdenum tailings sand on mechanical properties and microstructure of cement mortar. Five types of cement mortars with different substitution rates of molybdenum tailings sand were designed， and their workability， mechanical properties， and drying shrinkage properties were systematically tested. The microstructure and hydration products were analyzed using SEM and XRD. The results indicate that the saturated content point of water-reducing agent for both molybdenum tailings sand mortar and manufactured sand mortar is 5‰ of the total mass of cementitious materials， and the water retention of molybdenum tailings sand mortar is poorer. The compressive strength of mortar reaches its peak at a mass substitution rate of 50% for molybdenum tailings sand， while the flexural strength is optimal at a substitution rate of 25%. The drying shrinkage value increases significantly with the substitution rate， reaching a drying shrinkage value of 1 223×10^-6 at a substitution rate of 100% after 90 d. Microscopic analysis shows that an appropriate amount of molybdenum tailings sand can enhance the compactness through micro-aggregate filling effect and nucleation effect， but excessive substitution leads to grading deterioration and increased porosity. Molybdenum tailings sand can partially replace manufactured sand in cement mortar， and the recommended substitution rate is not more than 50% to balance mechanical properties and volume stability.

Key words: molybdenum tailings sand, cement mortar, manufactured sand, mechanical property, microstructure

CLC Number:

TQ177.6⁺2

RUI Zhenhua, LYU Xiangyu, GUO Can, HUANG Shan, NIU Dongyu. Influence of Molybdenum Tailings Sand Substitution Amount on Mechanical Properties and Microstructure of Manufactured Sand Cement Mortar[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2026, 45(2): 573-581.

Figures/Tables 12

Table 1 Main chemical composition of cement

Composition	SiO₂	Al₂O₃	Fe₂O₃	MgO	CaO	SO₃
Mass fraction/%	21.54	6.22	4.47	2.61	59.21	2.32

Table 2 Main chemical composition of molybdenum tailings sand and manufactured sand

Material	Mass fraction/%
Material	SiO₂	Al₂O₃	Fe₂O₃	MgO	CaO	TiO₂	Na₂O	K₂O
Molybdenum tailings sand	71.34	8.89	9.21	1.16	2.31	1.56	0.44	1.66
Manufactured sand	91.20	0.79	1.22	1.46	0.50	—	—	—

Table 3 Mix proportion of cement mortar

Sample No.	Mass/g
Sample No.	Cement	Water	Manufactured sand	Molybdenum tailings sand
M0	500	240	1 500	0
M25	500	240	1 125	375
M50	500	240	750	750
M75	500	240	375	1 125
M100	500	240	0	1 500

Fig.1 Saturated content point of mortar water-reducing agent

Fig.2 Mortar fluidity loss over time

Fig.3 Effect of molybdenum tailings sand substitution rate on mortar fluidity

Fig.4 Effect of molybdenum tailings sand substitution rate on compressive strength of mortar

Fig.5 Effect of molybdenum tailings sand substitution rate on flexural strength of mortar

Fig.6 Effect of molybdenum tailings sand substitution rate on drying shrinkage value of mortar

Fig.7 XRD patterns of mortar with different substitution rate of molybdenum tailings sand at 28 d

Fig.8 SEM image of manufactured sand mortar at 28 d

Fig.9 SEM images of mortar with different substitution rates of molybdenum tailings sand at 28 d

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