title: The Functional Properties of Travertine Pervious Concrete Pavement
Creators: name: Li, Tianzhen
Publisher: name: University of Liverpool Repository
Year: 2028

description: Rapid urbanization has led to an increase in urban impervious surfaces, causing more flooding problems. Cutting travertine generates a large number of debris and powder that is usually recognized as solid waste for landfills. Therefore, effective utilization of this solid waste deserves more attention. This study aims to develop pervious concrete pavements using travertine waste (TPCP) to address urban flooding and realize solid waste utilization. The main objective was to evaluate the physical, mechanical, hydraulic, microstructure, durability, and environmental performance of travertine pervious concrete (TPC) using the orthogonal test method to get the satisfactory C30/C20 TPC with high water permeability and excellent water purification ability. Ultimately, different lab-scale travertine pervious concrete pavements (TPCP) with a rainfall simulation system were built to evaluate their practical efficiencies.

The orthogonal results showed that travertine waste can be used as different sizes of aggregates for the preparation of C30/C20 TPC and increase its water permeability, which meets the requirements of standard CJJ/T135-2009. The damage pattern of TPC specimens showed significant partial or complete fracture of the travertine aggregate compared to that of the conventional aggregate pervious concrete, which was mainly damaged at the interfacial transition zone (ITZ). Besides, cement replacement with 5-10% travertine waste powder in TPC can satisfy engineering requirements, improve heavy metal adsorption ability, realize waste recycle, and lower CO2 emission. After 25 cycles, TPC still demonstrated excellent freeze-thaw resistance.

The heavy metal adsorption capacity of TPC was affected by many factors. The contact time between TPC and heavy metal solution directly affects the adsorption capacity of heavy metals. Travertine aggregates in pervious concrete can only remove up to 4.80% of heavy metal ions, mainly because the presence of cement paste prevents direct contact between aggregates and heavy metal ions. The removal rate of heavy metals was also affected by the contact area. Furthermore, the travertine aggregate can easily remove heavy metals due to its porosity and high mineral composition. Under the influence of a ternary competitive mechanism, the adsorption capacity of TPC for different heavy metal ions is Pb2+ &gt; Cd2+ &gt; Cu2+. 

High content waste powders (travertine and limestone powder) were added to the travertine pervious concrete to modify its properties. Waste travertine and limestone powder substituted for cement generally reduce the porosity, permeability, and compressive strength of pervious concrete but result in lighter pervious concrete, improve the heavy metal removal ability, and show good freeze-thaw resistance. Preparing TPC samples using 15% waste travertine and limestone powder was suggested to meet the design requirements of C30 pervious concrete pavement and significantly lower the use of cement materials and CO2 emissions. Furthermore, incorporating 3% fine sand in TPC was found to improve its mechanical and freeze-thaw properties and maintain a certain degree of permeability ability. 

Finally, the penetration efficiency of the C30 TPCP decreases with increasing input intensity from 5 to 15 L/min. The C30 TPCP can drastically reduce the runoff volume 72.17-96.23% in 60 minutes and remove more than 96% of Cd2+, Cu2+ and Pb2+ within 30 minutes. Another C20 TPCP can effectively reduce runoff, reaching over 96% within one hour. After half an hour, the removal rates of Cd2+ and Cu2+ by C20 TPCP were only 41.5 and 79.1%, respectively, but achieved exceptional Pb2+ adsorption with a removal rate of over 97%, demonstrating environmental friendliness.