Implications of increasing the ferruginous cement on the physical and mechanical properties of the Cambro-Ordovician Wajid Sandstone in southwest Saudi Arabia: applications for construction purposes

The main target of the present study is to characterize the physical and mechanical properties of the Wajid Sandstones in SW Saudi Arabia and to evaluate its economic value for construction purposes. A number of samples were collected representatively for the upper Gray ‘UGU’ and lower red ‘LRU’ units of the Wajid Sandstones from three sites in the area of study. The studied physical properties include porosity ‘∅’, capillary water absorption ‘Sw’ and bulk specific gravity ‘SP_G’, while the mechanical properties include the uniaxial compressive strength ‘UCS’, the ultimate tensile strength ‘UTS’, the Schmidt hammer number ‘RN’ and degree of Abrasion ‘Ab’. Petrographically, the studied Wajid samples are composed of fine to coarse quartz grains cemented by siliceous cement with some ferruginated cement in the ‘LRU’ unit. In addition, some samples were studied using the ‘SEM’ and ‘XRD’ analyses to reveal their mineral composition and homogeneity of their internal fabrics and cement type. The ‘XRD’ and SEM studies indicate that the ‘LRU’ samples are cemented by a ferruginated siliceous silica cement (8.12 ≤ hematite ≤ 13.96%) in the form of iron spherules attached to the pore and grain surfaces. Both the physical and mechanical values of the studied samples have given weights and ratings, and their quality index ‘QI’ was then calculated. The ‘QI’ values indicate that the sandstone samples of the ‘UGU’ unit are fair to poor (19.8 ≤ QI ≤ 22.5) at the different sites and not suitable for construction purposes. On the other hand, the ‘QI’ values of the ‘LRU’ samples are good (32.5 ≤ QI ≤ 37.6) and are suitable for construction purposes. A model has been introduced to predict in precise the ‘UCS’, ‘UTS’, ‘∅’ and ‘SP_G’ of the studied Wajid Sandstones during further quarrying. Statistical equations of the proposed model are characterized by very high reliability (0.876 ≤ R² ≤ 0.975). Finally, the areal extension of the studied fluvial silici-clastic deposits of the Wajid Sandstones have been traced through their regional extensions in the Arabian Peninsula and it has been stated that they are comparable with the Nubia sandstone sequences in NW Africa.