The Ordinary Portland Cement (OPC) is engineered using the agro waste derived graphene oxide (GO). GO was prepared from rice husk through phosphoric acid activation. The prepared GO was added into OPC at different weight ratio to study its impact on the mechanical properties. The functional groups, morphology and composition of the composites were studied using FTIR, SEM, and EDAX. Experimental results indicated that GO was dispersed in OPC composite. The mechanical properties of GO added OPC composites were studied. The results revealed that GO added cement composite shows relatively higher compressive strength compared to GO free OPC. Moreover, the compressive strength of OPC composite increased with GO content up to 0.04 wt.% and slightly decreased for the composite with 0.06 wt.% of GO. Hence, the prepared OPC composite with 0.04 wt.% GO was practically applied in rehabilitation and strengthening of a monumental building. An ancient temple has truncated pyramidal stone masonry tower with a brick masonry vault above. Lime mortar is used as binder. It is rehabilated and strengthened using the agro-waste derived GO-based OPC paste, corrosion resistant steel bars and meshes for strength and confinement. Brick masonry vault is given surface treatment and finishes with prepared composite. The results support to cure the damages in the monumental buildings and to preserve heritage.