Reading and understanding scientific texts is useful and necessary in many informal collaboration settings, including research or innovation collaborations, or when discussing public science in lay peer groups. In this work, we investigate whether an interactive predefined concept map that builds up gradually while reading a scientific research article helps teams of readers in their collaborative knowledge construction. The underlying assumption is that predefined concept maps as a visual knowledge representation complement the knowledge that is textually encoded in scientific articles. We present a randomized controlled trial that compares two conditions: In the intervention (n=50) and control (n=44) group, randomly matched pairs of university students read a scientific text, took notes, discussed the scientific text in real-time in a chat, and summarized the content of the scientific text. The intervention group additionally received the gradually built-up concept map while reading. We analyzed chat messages and the collaboratively written summary on the basis of knowledge construction theory, as well as time of task completion, thus studying the socio-cognitive processes stimulated by our intervention. We also compared study participants' knowledge pre/post-task. While the intervention and control groups did not differ significantly in their collaborative knowledge construction or individual knowledge gain, the intervention group was significantly faster at reading the text (F(1,92)=4.70, p=0.033) and required fewer notes (F(1,92)=6.66, p=0.011). The integration of predefined concept maps alongside scientific texts is technically simple. It could therefore be incorporated into different digital platforms, supporting collaborative reading of texts and improving the overall learning efficiency of readers.