The galvanic cathodic protection of steel embedded in concrete structures is enhanced by the utilization of a flexible composite anode assembly containing a sacrificial anode member. The anode member is at least partially covered by a matrix comprising an ionically-conductive material. The conductive material includes at least one electrochemical activating agent such as a mixture of lithium bromide and lithium nitrate and a compressible water-retaining mineral such as a phyllosilicate mineral. The presence of this mineral in the matrix increases the current delivered by the anode, thereby resulting in a greater level of cathodic protection, and a longer effective service life of the anode. Exfoliated vermiculite is a preferred phyllosilicate mineral and is present in an amount of between about 2% and about 15% by weight, based on the total weight of the matrix.