麻烦帮我看看这句话有没有语法错误

题目

麻烦帮我看看这句话有没有语法错误
Deterioration could lead to decreasing the minimum performance period of building materials,which means that the materials will not last till what it was expected to.

答案

这句子前半部大致没有问题
但what it was expected to就有保留
首先是it这个代名词
相信应当是指the materials
若是如此
应当用they
而且时式较宜用‘现在时’
再从整个短句来看
以改动最少的原则而言
可以考虑用2个方法来表达
其一是用when
即till when they are expected to
其二是用what
即till what they are expected of
(句子原为they are expected of sth,将sth用what代替,再调在开首而成)
所以不应用to,而是要用of
至於较大的改动
可参考oxd_bxo的方法
略为改成
Deterioration could cause the decrease in (the shortening of) the minimum performance period of building materials ,which means the materials will last shorter than they are expected.
或
Deterioration could decrease (shorten) the minimum performance period of building
materials ,which means the materials will last shorter than expected.
希望有达人在这问题上给意见