Abstract

Cathode ray tube(CRT)has been utilized to produce monitor displays in the past decades,and it is classified as a hazardous material because it contains lead[1-3].With the development of new display technology,the amount of obsolete CRT is growing dramatically.Most waste CRTs are disposed in landfill sites,and only approximately 26% are reused[4-5].The disposal of waste CRTs in landfills has significant drawbacks,as lead leakage can pollute water and soil and resu_lt in oral intake of lead by humans[6-8].Hence,waste CRTs should thus be carefully treated,and the proper recycling method of waste CRTs has attracted particular attention.However,the current recycling methods involve with either environmental pollution or limited recovery scale,bringing main challenges for waste CRT management.

In this paper,an innovative cementitious material[9-10],ultra-high performance concrete(UHPC)was introduced to combine and recycle hazardous waste CRT.Crushed CRT funnel glass was utilized to substitute river sand in various ratios in UHPC.The mechanical properties and toxic heavy metal leachability of UHPC were investigated,and the microstructure of UHPC was also observed.Test results indicate that the addition of CRT funnel glass can increase the flowability of UHPC,but decrease the compressive and flexural strength of UHPC.When the replacement ratio of CRT funnel glass is 25%,the flowability improves significantly while the mechanical properties reduce slightly(about 3%)compared to those of the reference group.Analyses by X-ray diffraction and electron microscopy scan demonstrate that CRT funnel glass inhibits cement hydration and weakens the interfacial transition zone,resulting in the reduced strengths of UHPC.Meanwhile,the toxicity characteristic leaching procedure of UHPC containing CRT funnel glass at 160 days was conducted,and the leached lead(Pb)concentration was displayed in Table 1.The leached lead concentration was only 3.35 mg/L even the replacement ratio of CRT funnel glass was 100%,which is below the regulatory limit(5 mg/L)of United States Environmental Protection Agency.It can be concluded that the lead leaching of hazardous CRT glass was effectively inhibited in UHPC.The mechanism behind was that the dense microstructure and low permeability coefficient of UHPC significantly restrained the lead leaching process.Moreover,the leached concentrations of other heavy metals were also listed in Table 1,including Cr,Zn,Ba,Cd,Ni,Cu and As.It was shown that the leached concentrations of those heavy metals at 160 days were far below the regulation limit.

Table 1　Concentrations of leached heavy metals of UHPC incorporated with CRT gla ss at 160 days(unit:mg/L)

Note:—indicates below the detection limit(＜0.001 mg/L).

The material design(UHPC and hazardous waste CRT)in this paper provided an effective alternative to recycling hazardous waste CRT on a large scale without limitations on the replacement ratio and safety concern,as well as paves the way for a sustainable UHPC.