Precast and cast-in-situ structures made of reinforced concrete are widely used in construction today, so it is vital to ensure reliable adhesion of newly poured (“new”) and already set (“old”) concrete. The paper means of ensuring the necessary adhesion strength of new and old concrete for construction joints and for joints in precast structures. We studied the contact area of a new concrete layer with the concrete base using several methods, including standard methods. The obtained data indicate the pH effect of the new medium on the adhesion strength of the new concrete to the base of the old concrete, as well as the compressive and shear strength of the concrete in the contact area between the newly poured and previously poured concrete. The paper analyzes the obtained results and compares them with data from previous studies. The formulated conclusions can be used to improve concrete adhesion strength in precast and cast-in-situ reinforced concrete structures.