An assessment on volume stabilization of mortar with stainless steel slag sand

•A mixture mortar was developed using pre-treated stainless steel oxidizing slag as aggregate.•Free lime content existing on treated slag was determined for each month.•Expansion of the mortar were measured using autoclave and heating catalysis methods.•Effects of replacing level and pre-treatment periods of slag on mortar were investigated.•Relationships between compressive strength and UPV on the specimens were established. This study aims at employing stainless steel oxidizing slag (SSOS) as fine aggregate, replacing river sand in mortar mixtures with various ratios (e.g. 0%, 25%, 50%, 75%, and 100%). The received slag was left outdoor from 1- to 8months as a treatment before be used as aggregate. The content of slag expansion source (free lime) was first determined after the end each month of stabilization. The X-ray diffraction (XRD) technique was offered to identify the mineralogical of the treated slag. Next, fresh and hardened properties of the stabilized-slag mortar including flow table, expansion, compressive strength, ultrasonic pulse velocity were examined in laboratory, accordingly. The expansion in term of length change of the slag mortar bars (25×25×285mm) was investigated after the autoclave and heating catalytic (100°C) curing conditions. The results indicated that free lime content is gradually decreased over times when SSOS exposed to air environment and effectively restricted the expansion capacity of the slag mortar. In addition, a higher SSOS replacement ratio a larger expansion is measured on the mortar bars. Meanwhile, a lesser period of slag treatment could make the specimens fracture at a lower level of slag substitution. The expansion of mortar bar under the autoclave is similar to that of about 72–96h heating catalysis. Moreover, compressive strength of mortar is improved when containing as much as slag in mixtures, although this induces less workability of fresh mortar.