Concrete usually possesses advantages of high compressive strength but weaknesses of low tensile strengthoriginating from the intrinsic brittleness of cement hydrates. Here we propose a method ofin situcopolymerization ofmonomers that use acrylic acid (AA) and acrylamide (AM) to restrain the brittleness of cementhydrates byin situcopolymerization during cement hydration and to enhance the mechanical strength of the cement matrix. Cement pasteswith reinforced flexural strength and compressive strength can be obtained by modulating the fraction of AA-AMcopolymer. With the polymerization reaction, a polymer skeleton was constructed in the cement matrix, followed bycrosslinking with cement hydrates by the coordination between metal ions (Ca2þand Al3þ) and carboxy groups, enhancingthe flexural strength and toughness of cement pastes. Our work offers a straightforward method to reduce the intrinsicbrittleness of cement hydrates, providing a facile access to cementitious materials with improved flexural performance.