Reinforcement bar for concrete structures, comprising - a plurality of continuous, parallel fibers, made of basalt fiber, tensioned and embedded in a cured matrix, each bar has - an average length in the range 20 mm to 200 mm, and - an average diameter in the range 0.3 mm to 3 mm, where at least a part of the surface of each bar is deformed by means of: - one or more strings of a tensioned material helically wound around said plurality of parallel fibers, maintaining the fibers in a parallel state, characterized in that said string forms helically extending indents in a continuous manner along the length of the bar, and the surface of the bar is given a helically arranged convex outer surface, wherein - an angle α is the angle between the helically wound string and the centerline of the bar and is in the range from 4 to 8 degrees, - an angle β is the angle between the centerline of the bar and the longitudinal direction of the fibers and is in the region between 2 to 5 degrees, - the pitch length of the helically wound string is in the range of 10 mm to 22 mm, and/or - that said bar is provided with a roughened surface shape and/or texture contributing to good bonding with the concrete, where the weight factor of the fibers in respect to the weight factor of the matrix is in the range of 65 to 85. - a plurality of continuous, parallel fibers, made of basalt fiber, tensioned and embedded in a cured matrix, each bar has - an average length in the range 20 mm to 200 mm, and - an average diameter in the range 0.3 mm to 3 mm, where at least a part of the surface of each bar is deformed by means of: - one or more strings of a tensioned material helically wound around said plurality of parallel fibers, maintaining the fibers in a parallel state, - one or more strings of a tensioned material helically wound around said plurality of parallel fibers, maintaining the fibers in a parallel state, characterized in that said string forms helically extending indents in a continuous manner along the length of the bar, and the surface of the bar is given a helically arranged convex outer surface, wherein - an angle α is the angle between the helically wound string and the centerline of the bar and is in the range from 4 to 8 degrees, - an angle β is the angle between the centerline of the bar and the longitudinal direction of the fibers and is in the region between 2 to 5 degrees, - the pitch length of the helically wound string is in the range of 10 mm to 22 mm, and/or - that said bar is provided with a roughened surface shape and/or texture contributing to good bonding with the concrete, where the weight factor of the fibers in respect to the weight factor of the matrix is in the range of 65 to 85. - an angle α is the angle between the helically wound string and the centerline of the bar and is in the range from 4 to 8 degrees, - an angle β is the angle between the centerline of the bar and the longitudinal direction of the fibers and is in the region between 2 to 5 degrees, - the pitch length of the helically wound string is in the range of 10 mm to 22 mm, and/or - that said bar is provided with a roughened surface shape and/or texture contributing to good bonding with the concrete, where the weight factor of the fibers in respect to the weight factor of the matrix is in the range of 65 to 85.