Analysing the life index of diamond cutting tools for marble building stones based on laboratory and field investigations

Cutting tool wear constitutes one of the principal parameters in the processing cost of building stone. The life index of the cutting tool is obtained by evaluating the wear of diamond segments in the processing plants and examining the main parameters thereof. The purpose of this study is to determine the life index of the diamond cutting tool by considering the physico-mechanical properties of marble stones and the operational parameter of cutting speed. To this end, a dataset was provided by collecting the data from eight building stone processing plants in the provinces of Tehran, Isfahan, and Yazd of Iran. In this regard, the number of square metres of building stone that every diamond cutting tool can cut during its lifetime is defined as the cutting tool life index (TLI). After collecting the required data, SPSS software was employed for statistical analysis. The results revealed that the Brazilian tensile strength is the main parameter that affects the cutting tool life index. Linear and non-linear regression analyses were then considered for the development of predictive models for the TLI based on the Brazilian tensile strength. The performance of the developed models was subsequently examined by using three different criteria: the coefficient of determination, the variance accounted for, and the root-mean-square error. The results of this study show that the non-linear predictive model of the TLI presents a very good performance, and thus, the diamond cutting tool life index can be obtained for marble stones by considering the model developed herein.

The effect of saturation on the physical and mechanical behavior of some rock samples

Different major factors control the strength of solid rocks. Moisture content is one of the most important factors, which can change the physical and mechanical behavior of intact rock as well as rock mass. Several early studies have shown that rock is weaker if tested wet rather than dry. In this paper, the density, P-wave velocity, uniaxial compressive strength, Brazilian tensile strength, and modulus of elasticity of seven different intact rock samples were measured under both dry and saturated conditions. The porosity of the samples was reported as well. Based on the obtained results, some correlations were proposed for estimating the saturated physical and mechanical properties from dry ones. The proposed correlations include different rock types and are more general than the previously reported ones. Comparing the obtained results showed that the mechanical and physical properties of weaker samples are more sensitive to the saturation process. Moreover, among the different mechanical parameters, Brazilian tensile strength exhibited more sensitivity to saturation. Comparing the results with the calculated porosities revealed that porosity is one of the key factors in the effect of saturation on physical and mechanical parameters. It seems that in the more porous rock samples, greater changes in the different measured parameters occur after saturation.

The Relationship between Strength and Abrasion Characterizations in Granite Building Stones

The wear of cutting blades during the preparation of building stones is an inevitable issue that occurs due to the contact of the blade with rock components. The present study aims to investigate the feasibility of proposing experimental relations of strength parameters and mineralogical hardness with Cerchar and LCPC tests. For this purpose, 18 samples of granite building stones were selected and Equivalent Quartz Content (EQC), compressive and Brazilian tensile strength (UCS and BTS), Cerchar, and LCPC abrasivity indices (CAI and LAC) were determined. The results showed the lack of any significant relationship between strength and abrasion properties. However, when evaluating the simultaneous impact of EQC and UCS using the rock abrasion index (RAI=UCS×EQC), significant valid empirical relationships between RAI-CAI and RAI-LAC were derived. To investigate the simultaneous effect of UCS, BTS, and EQC, a dimensionless parameter, i.e. modified rock abrasion index (MRAI=(UCSBTS)×EQC) was introduced. Moreover, it was found that the empirical relationship between MRAI-CAI was more significant and valid than the previous relations. Verification of the proposed relationship with the values of other researchers and 6 new samples for estimating CAI and LAC based on UCS, BTS, and EQC was found to be highly accurate for granite building stones.

Hemp Fiber Reinforced Red Mud/Fly Ash Geopolymer Composite Materials: Effect of Fiber Content on Mechanical Strength

Novel hemp fiber reinforced geopolymer composites were fabricated. The matrix was a new geopolymer based on a mixture of red mud and fly ash. Chopped, randomly oriented hemp fibers were used as reinforcement. The mechanical properties of the geopolymer composite, such as diametral tensile (DTS) (or Brazilian tensile) strength and compressive strength (CS), were measured. The geopolymer composites reinforced with 9 vol.% and 3 vol.% hemp fiber yielded average DTS values of 5.5 MPa and average CS values of 40 MPa. Scanning electron microscopy (SEM) studies were carried out to evaluate the microstructure and fracture surfaces of the composites. The results indicated that the addition of hemp fiber is a promising approach to improve the mechanical strength as well as to modify the failure mechanism of the geopolymer, which changed from brittle to “pseudo-ductile”.

AN INVESTIGATION ON THE EFFECTS OF MICRO-PARAMETERS ON THE STRENGTH PROPERTIES OF ROCK

Rocks are formed from particles and the interaction between those particles controls the behaviour of a rock’s mechanical properties. Since it is very important to conduct extensive studies about the relationship between the micro-parameters and macro-parameters of rock, this paper investigates the effects of some micro-parameters on strength properties and the behaviour of cracks in rock. This is carried out by using numerical simulation of an extensive series of Uniaxial Compressive Strength (UCS) and Brazilian Tensile Strength (BTS) tests. The micro-parameters included the particles’ contact modulus, the contact stiff ness ratio, bond cohesion, bond tensile strength, the friction coefficient and the friction angle, and the mechanical properties of chromite rock have been considered as base values of the investigation. Based on the obtained results, it was found that the most important micro-parameters on the behaviour of rock in the compressive state are bond cohesion, bond tensile strength, and the friction coefficient. Also, the bond tensile strength showed the largest effect under tensile conditions. The micro-parameter of bond tensile strength increased the rock tensile strength (up to 5 times), minimized destructive cracks and increased the corresponding strain (almost 2.5 times) during critical stress.

Characterization of the Petrographic and Physicomechanical Properties of Rocks from Otanmäki, Finland

Intact rock properties are important for mining and geotechnical engineering because they are important design parameters for tunnels, rock foundations, rock slopes, among others. Some of the properties are also used as input parameters in some rock mass classification systems. Therefore, as rock properties are site-specific, there is need to investigate rock properties at a site especially when such site is used for engineering purpose. This paper documents the petrographic and X-ray fluorescence analyses, and physical and mechanical tests conducted to estimate the physical and mechanical properties of the two rock types (i.e. gabbro and granite) selected from quarries at Otanmäki, Finland. Mineral composition, grain size and chemical composition, water content, porosity, Brazilian tensile strength, uniaxial compressive strength, Young’s modulus, and Poisson ratio of the rock types were determined. Both gabbro and granite samples have fine to medium grained texture. The results of laboratory experiments conducted show that rock properties investigated have low to high variability. Simple and multiple regression analyses were performed and useful predictive models for estimating Brazilian tensile strength from physical test results were developed and validated.