How do you clean concrete grouting in a tile lined shower ?

Try a half cup of baking soda to a gallon of water. Add 1/8 cup of dish soap and spray on the shower. Let it sit for 30 minutes, then scrub and rinse.

How to Clean Grout

https://www.hgtv.com/lifestyle/clean-and-organize/clean-shower-tile-grout

For dirty grout, sprinkle baking soda on then spray hydrogen peroxide, give it a light scrubbing and wash away. Avoid vinegar as it will etch and dissolve both concrete and grout.

I use clorox cleanup it has a small amt of bleach in it and sometimes I have to use a grout brush to scrub some of the stubborn mildew out - I rinse well and in the 31 yrs in my home I have never had issues with it eating the grout/cement

I forgot to say that if you will leave your shower door open after you shower that will help air to circulate more in your shower and keep down mold/mildew as well and we use a squegee on the tile walls after showers which helps too-

White vinegar will kill mold spores. I would use Wet & Forget Shower weekly for regular cleaning. As preventive measures, rinse with hot water when you get out, leave the door or curtain open, use a fan to circulate the air, leave the room door open as well.

Here's what I use:

• 1/2 cup baking soda
• 1/4 cup hydrogen peroxide
• 1 teaspoon dish soap
• Medium bowl
• Sponge
• Scrub brush

Hello M. clean the grout using a vinegar and baking soda mix, Apply a baking soda paste and spray with vinegar.

To bring even more cleaning power to the party, cover grout lines with a paste of baking soda and water, then spray on the vinegar solution listed above. Once the mixture stops foaming, scrub with a brush and rinse with plain water.

Once you get it clean and dried, you can seal the grout to prevent it from getting discolored and mildewed,

https://theflooringgirl.com/blog/grout-sealer-importance-diy/

All kinds of ways

https://www.hometalk.com/search/posts?filter=clean%20grout

Make a paste using baking soda and hydrogen peroxide. Using a grout brush or toothbrush, spread the paste over the grout, working it into the grout. Let it sit for 30 minutes or longer, re-moisten with warm water if needed, and scrub away the mold. Rinse the paste away with warm water and repeat if needed.

I have done the above paste as well and it worked well. But because I have a bad knee it is hard for me to get down to use a brush or toothbrush to put it on the grout, instead I used a stiff bristle broom or long handled brush to scrub it on and off. Worked great.