Properties Of Cemented Paste Backfill Research Articles

Strength and ultrasonic properties of cemented paste backfill

This paper presents the strength (UCS) and ultrasonic pulse velocity (UPV) properties of cemented paste backfill (CPB) produced from two different mill tailings (Tailings T1 and T2). A total of 240 CPB samples with diameter×height of 5×10cm and 10×20cm prepared at different binder dosages (5–7wt.%) and water-to-cement ratios (3.97–5.10) were subjected to the UPV and UCS tests at 7, 14, 28 and 56-days of curing periods. UCS and UPV of CPB samples increased with increasing the binder dosage and reducing the w/c ratio irrespective of the sample size and tailings type. CPB samples with a diameter×height of 5×10cm were observed to produce consistently higher (up to 1.69-fold) UCSs than those of 10×20cm CPB samples at all binder dosages and w/c ratios. However, at the corresponding binder dosages and w/c ratios, the maximum variation of UPV between the CPB samples of 5×10cm and 10×20cm was only 7.45%. Using the method of least squares regression, the UCS values were correlated with the UPV values for CPB samples of 10×20cm in size. A linear relation with a high correlation coefficient appeared to exist between the UCS and UPV for CPB samples. These findings suggest that the UPV is essentially independent of the sample size. In this regard, the UPV test can be suitably exploited for the rapid estimation of the strength and quality of CPB samples even using small samples with concomitant benefits of reducing sample size.

The effect of solid components on the rheological and mechanical properties of cemented paste backfill

An experimental study is conducted to investigate the effect of solid components on the rheological and mechanical properties of cemented paste backfill (CPB). Based on the paste consistency, 78wt.% could be a critical value for the solid contents. The mechanical strength increased proportionally with the increase of solid contents. The paste backfill samples prepared with 80wt.% solid contents have a maximum unconfined compressive strength (UCS) of 7.26MPa at a curing time of 28days. A large binder proportion could weaken the consistency of the paste. The slump height drops from 27.5 to 23.5cm when the bind proportions increase from 6.25wt.% to 25wt.%. The long-term mechanical performance increases significantly as the binder proportion increased. The UCS of the CPB sample with 8.33wt.% binder is five times larger than the sample with 6.25wt.% binder. A 25wt.% addition of ungrounded slag causes the slump height to drop from 13 to 25.4cm, mainly due to the decrease in the friction and void spaces between particles. However, the addition of coarse slag would weaken the mechanical properties of the CPB. The UCS of the samples without slag is almost two times larger than the UCS of the samples with 25% slag addition. The addition of soluble glass to the paste mixture appeared to improve the initial setting process. The initial setting time decreases from 846 to 108min when the accelerator addition increases from 1.1wt.% to 3.3wt.%.

Thermal conductivity of cemented paste backfill material and factors affecting it

Cemented paste backfill (CPB) is extensively used in underground mine operations. Several studies have been conducted to investigate the mechanical properties of CPB. However, little attention has been devoted to the thermal conductivity of CPB. The knowledge of this thermal property is vital for the design of cost-effective and durable CPB materials. This article presents the results of a comprehensive laboratory study on the thermal conductivity of CPB. Influencing factors on the thermal conductivity of CPB were quantitatively investigated. The measurements of thermal conductivity were performed by using the KD2 Thermal Properties Analyser. Valuable results with regards to the effects of CPBs mix components, curing time and temperature, and water saturation degree on the thermal conductivity of CPB were gained. It is felt that the present study would contribute to the better optimisation of CPB mixtures and the design of more cost-effective and durable CPB underground structures.

Effect of high temperature on strength and microstructural properties of cemented paste backfill

The main purpose of this research is to investigate the influence of high temperatures on the strength and microstructure (e.g. pore structure, porosity) of cemented paste backfill (CPB) through a series of experimental tests. A laboratory experimental setup allowing the simulation of various high-temperature conditions is developed. Different types of CPB specimens are exposed to different high temperatures (100, 200, 400 and 600 °C). The strength, porosity, pore size distribution and water absorption of these CPB specimens are then evaluated by laboratory tests. Thermogravimetric and differential thermal analyses are also performed to study the thermal behaviour of the CPBs exposed to high temperatures. The results show that high temperatures have a significant effect on the properties of CPBs. Generally, increasing temperatures up to 200 °C leads to higher strength in most types of CPB studied. The porosity and pore size distribution of the CPBs change only slightly. Above 200 °C, the temperature reduces the strength of the CPBs. The most notable strength decrease takes place at exposure temperatures exceeding 400 °C. The significant decrease of the strength of the CPB is accompanied by a significant change in the microstructure (porosity, pore size distribution, mineral phases). Moreover, the effect of high temperatures on the strength and microstructure of CPBs depends on the water/cement ratio (w/c ratio) and the tailings type.