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 empty set', capillary water absorption Sw' and bulk specific gravity SPG', 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 (8.12hematite13.96%) 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 (19.8QI22.5) at the different sites and not suitable for construction purposes. On the other hand, the QI' values of the LRU' samples are good (32.5QI37.6) and are suitable for construction purposes. A model has been introduced to predict in precise the UCS', UTS', empty set' and SPG' of the studied Wajid Sandstones during further quarrying. Statistical equations of the proposed model are characterized by very high reliability (0.876R(2)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.