混凝土，又称洋灰或者石矢（在中国大陆书面上又写作砼)（拼音：tóng、注音：ㄊㄨㄥˊ），是由胶凝材料、骨料和水按适当比例配置，再经过一定时间硬化而成的人工石材。混凝土的硬度高、坚固耐用、原料来源广泛、制作方法简单、成本低廉、可塑性强、适用于各种自然环境，是世界上使用量最大的人工土木建筑材料，广泛使用于房屋、桥梁、公路、跑道、挡土墙、堤防、涵洞、水坝、水箱、水塔、油槽、渠道、水沟、码头、防波堤、军事工程、核能发电厂等构造物。

Concrete is a composite material composed of coarse aggregate bonded together with a fluid cement which hardens over time. Most concretes used are lime-based concretes such as Portland cement concrete or concretes made with other hydraulic cements, such as ciment fondu. However, road surfaces are also a type of concrete, asphalt concrete, where the cement material is bitumen, and polymer concretes are sometimes used where the cementing material is a polymer.